The Journal of Arthroplasty 30 (2015) 2110–2115
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Resection Technique Does Affect Resection Symmetry and Thickness of the Patella During Total Knee Arthroplasty: A Prospective Randomized Trial Christopher L. Camp, MD , John R. Martin, MD, Aaron J. Krych, MD, Michael J. Taunton, MD, Luke Spencer-Gardner, MD, Robert T. Trousdale, MD Department of Orthopedic Surgery, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
a r t i c l e
i n f o
Article history: Received 27 March 2015 Accepted 21 May 2015 Keywords: total knee arthroplasty patellar resurfacing patellar resection knee arthritis patellofemoral joint
a b s t r a c t The purpose of this study was to evaluate the accuracy and efficiency of three patellar resection techniques: cutting guide, free hand with haptic feedback, and a novel technique utilizing four quadrant measurements. Ninety patients undergoing TKA were randomized to receive patellar resurfacing by one of the three study techniques. The novel four quadrant technique resulted in least post-resection asymmetry (0.85 mm, P = 0.001). The most accurate methods for obtaining desired thickness were haptic feedback (0.66 mm mean discrepancy [MD]) and novel four quadrant technique (0.66 mm MD) followed by the patellar cutting guide (1.40 mm MD) (P b 0.001). Use of a patellar cutting guide resulted in increased patellar asymmetry and decreased accuracy in obtaining desired patellar thickness in this prospective trial. © 2015 Elsevier Inc. All rights reserved.
Resurfacing of the patella during total knee arthroplasty (TKA) is a commonly performed procedure. Numerous randomized studies have attempted to determine the necessity of patellar resurfacing in the setting of a primary TKA [1–7]. These studies looked at factors believed to increase revision rates including: anterior knee pain, knee functional scores, patellar fractures, and patellar maltracking. Although a general consensus has not yet been reached on this topic, the majority of surgeons in the US routinely resurface the patella during primary TKA. Accordingly, a number of principles in patellar resection should be considered including: restoration of patellar height, performing symmetric resection, avoiding under-resection, and minimizing overstuffing of the patellofemoral joint [8]. The significance of this has been evaluated by examining complications associated with poor resection techniques such as 1) patellar fracture, 2) patellar maltracking, and 3) disruption of the extensor
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.05.038. Source of funding: Financial support for the statistical analysis and study coordination was obtained solely from internal funding. Level of Evidence: I. Prospective randomized controlled trial. Reprint requests: Christopher L. Camp, M.D., Mayo Clinic, 200 First St., SW, Rochester, MN, 55905. http://dx.doi.org/10.1016/j.arth.2015.05.038 0883-5403/© 2015 Elsevier Inc. All rights reserved.
mechanism [8–12]. Asymmetric resurfacing may lead to increased anterior knee pain, instability, and revision rates [10]. Due to these complications, a number of techniques have been described in an effort to optimize patient outcomes. Some advocate a haptic method, in which the surgeon estimates the patellar resection thickness and symmetry by feel while referencing anatomic landmarks such as the insertion sites of the quadriceps and patellar tendons [13]. The use of patellar resection cutting guides or jigs is another popular method utilized by many surgeons [14]. Recently, a novel freehand resection technique in which the posterior surface of the patella is divided into quadrants has been described [15]. Ring tipped calipers are utilized to determine the height of the remaining patella in each quadrant and the patella can then be accurately resected to the desired level based on these measurements. At our institution all three methods are routinely used for patellar resection. Patellar complications during TKA continue to be a problem affecting approximately 7% of patients undergoing primary TKA [16]. Although various studies have described individual results of patellar resections methods, none have attempted to compare the efficacy of various techniques in a head to head fashion. The following randomized prospective trial compares three commonly used patellar resection techniques: the use of a patellar cutting guide, haptic feedback, and the four quadrant technique. The main purpose of this study was to determine the most efficient method to symmetrically resurface the patella to the desired thickness during primary TKA. Additionally, this study assesses surgeon efficacy in patellar resection when learning a new technique as compared to their historically preferred method.
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♦ ♦ ♦
Fig. 1. Flow chart illustrating patient enrollment.
Materials and Methods After approval from our institution’s internal review board and our department’s orthopedic research review committee, a total of 90 patients undergoing TKA were prospectively enrolled into this randomized controlled trial (registered at www.clinicaltrials.gov) prior to surgery (Fig. 1). To be considered for the study, patients had to meet the following inclusion criteria: undergoing elective primary TKA with patellar resurfacing, willing to participate, and able to provide informed consent. Patients were excluded if they were undergoing revision TKA, were not definitively having their patella resurfaced at the time of TKA, or were unable or unwilling to provide informed consent. All surgeries were performed by one of three experienced arthroplasty surgeons (AJK, MJT, and RTT) who each enrolled a total of 30 patients (total n = 90). Within each of these three subgroups (A, B, and C) of 30 patients, patients were equally randomized to have their patella resected by one of the following three techniques during TKA: 1) use of a standard cutting guide, 2) freehand resection with haptic feedback or 3) freehand resection guided by four quadrant measurements. A total of 10 patients per surgeon were randomized to each technique. This resulted in 30 patients randomized to each technique across all surgeons (Table 1). Each of the three surgeons was familiar with all three resection techniques; however, they each preferred one of the techniques over the other two and historically performed the vast majority of their patellar resections in that manner. Prior to the study, no two surgeons preferred the same technique (Table 1). As a result, each surgeon was more
experienced with their own preferred resection method, but they had at least used the other two techniques previously. Informed consent was obtained from all patients in the clinical setting during their pre-surgical appointment. Randomization was completed by envelope system by an independent member of the study team that did not participate in the surgery or data collection (CLC). Each surgeon was provided with 30 sequentially numbered envelopes (1 through 30) that each contained a single data collection sheet. Surgeons were not allowed to open the envelopes until they were in the operating room. The technique to be performed was indicated on the data sheet in addition to the outcome measures. All procedures were performed entirely by the staff surgeons and they were timed from
Table 1 Patient Allocation. Cutting Guide Resections Performed by Surgeon A Resections Performed by Surgeon B Resections Performed by Surgeon C
10
a
Haptic Feedback 10
10
10
10
10
4 Quadrant 10
a
10 10a
A total of ninety patients were enrolled. There were thirty patients per surgeon and thirty patients per technique. a Indicates the surgeon’s historically preferred technique.
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who completed the resection. This was not timed. The difference between the thickest and the thinnest measurements was reported as the value of asymmetry. Ability to obtain resection goal was calculated by taking the difference between the surgeon’s previously stated goal and the average thickness of the four quadrants measured by the resident or fellow. If so inclined, the surgeon was allowed to revise the resection as needed using any technique of their choosing after all final study measurements were made by the resident or fellow. Standard onlay type patellar prostheses were used in all patients. Descriptions of Techniques
Fig. 2. Four quadrant method for assessing patellar resection symmetry and thickness.
start (first measurement of native patellar thickness) to finish (final measurement of resected patella). Outcome measures included patient demographic data such as age, gender, operative side, surgical indication for TKA, and implant type. Intraoperative outcome measures included: pre-resection thickness, goal for post-resection thickness, symmetry of resection, obtainment of resection goal, and time to complete the resection. Medial parapatellar arthrotomies were used for all patients. Each patellar resection procedure began by exposing the articular surface of the patella. Once the patella was fully exposed and the surgeon measured native patellar thickness, the timer was started. The surgeon would subsequently state their goal for post resection thickness (typically the thickness of the implant), and these values were recorded. The resection was performed according to randomized study technique. After the final resection, the timer was stopped. Post-resection symmetry of the patella was independently assessed by a resident or fellow who was not involved in the resection. This was evaluated by dividing the patella into four equal quadrants and measuring the thickness in the center of each quadrant using a ring tipped or “C” shaped caliper (Fig. 2) [15]. To reduce bias, post resection assessment was not performed by the staff surgeon
Standard Cutting Guide The native patellar thickness was measured using flat tipped calipers (Fig. 3A) and the goal for post resection thickness was noted. The cutting guide was set to the desired resection depth and applied in a symmetric fashion using the articular surface, anterior surface, and the insertion points of the quadriceps and patellar tendons for reference (Fig. 3B). The resection was made through the slot of the guide with a saw (Fig. 3C). The guide was removed, but surgeons were permitted to reapply the guide to recut the patella if they felt that additional resection was required. The patellar trial was placed and the restored thickness was measured (Fig. 3D). Freehand Resection, Haptic Feedback Native thickness was measured (Fig. 4A), and post resection goal was stated. The patella was resected in a freehand manner with an oscillating saw (Fig. 4B), and the surgeon judged symmetry based on haptic feedback (Fig. 4C) and thickness by measuring the anterior to posterior distance in the center of the patella. The resection was repeated as necessary until the desired thickness and symmetry were obtained. The patellar trial was placed and overall thickness was measured (Fig. 4D) [13]. Freehand Resection, Four Quadrant Measurements Native patellar thickness was measured (Fig. 5A). Post resection thickness goal was stated, and the resection was performed freehand (Fig. 5B) using an oscillating saw and anatomic landmarks as a guide. The patella was divided into four quadrants and thickness was
Fig. 3. Standard cutting guide technique. The native patellar height is measured (A). The guide is applied (B) and the resection performed (C). Final height is measured with the prosthesis in place (D).
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Fig. 4. Freehand resection haptic feedback technique. The native patellar height is measured (A). Freehand resection is performed (B) and the symmetry and height are assessed using haptic feedback (C). Final height is measured with the prosthesis in place (D).
measured in the center of each quadrant using ring tipped or “C” shaped caliper (Fig. 5C). Resection was repeated based on these four measurements as needed until satisfactory symmetry and resection were obtained. The patellar button was placed and overall thickness was assessed (Fig. 5D) [15]. Statistical Analysis Prior to enrollment, an a priori power analysis was conducted using radiographic data from postoperative merchant view x-rays on a
historical sample of 29 subjects who had previously undergone TKA with patellar resurfacing. In this cohort, patellar thickness was measured radiographically at the central border of the medial and lateral quartiles of the patella (Fig. 6). The mean discrepancy between these measures was 1.1 mm (standard deviation 0.68 mm). Assuming that similar variability would be observed in this study, a sample of 30 subjects per each of the three study groups (90 total) would provide 90% power to detect a difference in means between any two of the three groups of at least 0.6 mm (α = 0.05, two-sided test). Although postoperative merchant view x-rays may not provide equivalent accuracy
Fig. 5. Freehand resection quadrant measurement technique. The native patellar height is measured (A). Freehand resection is performed (B) and the symmetry and height are assessed in the center of all four quadrants of the resected surface (C). Final height is measured with the prosthesis in place (D).
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Fig. 6. Comparison of discrepancy in asymmetry and difference from goal for each technique.
compared to intra-operative measurement of patellar thickness, it was felt that it would be a reasonable surrogate for power analysis. Statistical analysis focused on: time to complete the procedures, discrepancy between the largest and smallest thickness measurements from the four quadrants of the resurfaced patella, and the discrepancy between mean post resection thickness and surgeon goal. Data are presented as means with ranges and standard deviations (SD) where appropriate. Since these differences represented means of normally distributed continuous variables, an analysis of variance (ANOVA) was used when comparing the three study techniques and a student t test was used when comparing surgeons’ historically preferred methods to the techniques that they were less experienced with. All statistical tests were two-sided and P values less than 0.05 were considered statistically significant.
they were less familiar with. Surgeon A historically preferred technique 1 (cutting guide); Surgeon B preferred technique 2 (haptic feedback); and Surgeon C preferred technique 3 (four quadrant). The 30 patients that underwent resection by their surgeon’s historically preferred technique made up one group and the other group was composed of the 60 patients who received patellar resurfacing by a technique that their surgeon was less experienced with (Table 3). No statistically significant differences were noted in patellar asymmetry (1.10 [SD 0.62] versus 1.44 [SD 1.07] mm; p = 0.111) or obtainment of surgeon goal (0.69 [SD 0.61] versus 1.01 [SD 0.93]; p = 0.091; Table 3). Surgeons were able to execute their preferred techniques in less time than the new techniques (92 [SD 37.8] versus 124 [SD 67.5] s; p = 0.018).
Results The three senior authors each performed 30 patellar resurfacings during primary TKA on a total of 90 patients over a 12 month period. There were 42 males and 48 females in the cohort with a mean age of 67.6 years (range, 42–86 years). The surgical diagnosis was osteoarthritis in all patients and 41 surgeries were right sided while 49 were left. Each surgeon performed each of the three study techniques a total of 10 times. The mean asymmetry for Group One (standard cutting guide) was 1.73 mm (range 0–4 mm; SD 1.04) while Group Two (Haptic Feedback) was 1.40 mm (range 0–3 mm; SD 0.88) and Group Three (Four Quadrant) was 0.85 mm (range 0–2 mm; SD 0.73) (Table 2). The four quadrant technique was found to most accurately produce symmetric patellar resections (p = 0.001) (Fig. 6). The difference between surgeon goal and actual resection height for each method was: cutting guide 1.40 mm (range 0–4.5 mm; SD 1.04), haptic feedback 0.66 mm (range 0–2.25 mm; SD 0.64) and four quadrant method 0.66 mm (range 0–2 mm; SD 0.59)(p b 0.001; Table 2). Each procedure was timed from the first measurement of native thickness made by the surgeon to the completion of their last resection. The time values did not differ significantly for the three techniques (p = 0.240; Table 3): cutting guide 128 s (range 22–311 s; SD 76.8), haptic feedback 102 s (range 48–180 s; SD 34.7), and four quadrant 110 s (range 40–280 s; SD 62.5) (Fig. 6). Surgeons’ performance utilizing their historically preferred technique was compared to their performance on the two techniques that
Patellar complications resulting from poor technique (fracture, extensor mechanism disruption, and maltracking) are not uncommon following TKA with a reported incidence of 7% [9,10,16]. In an effort to minimize these complications, attention should be directed towards optimizing resection symmetry, avoiding over or under resection, and resurfacing the patella in a timely manner. The current study is the first randomized prospective trial to evaluate three techniques commonly used for patellar resurfacing in an attempt to determine the most efficient manner to create a symmetrically resected patella of the appropriate thickness. Of the techniques studied, the four quadrant technique produced the most accurate patellar resections. Achieving the intraoperative goal for patellar thickness was most reproducible with the haptic feedback and four quadrant techniques compared to the standard cutting guide. These freehand techniques allow frequent and easy assessment of thickness and symmetry during the resection process. The cutting guide has the benefit of producing a smooth and even cut when cutting through the slot; however, it is dependent on the surgeon’s ability to apply the guide at the appropriate depth and obliquity. Another limitation of the guide is that it is difficult to fully evaluate the effectiveness of the resection without removing it. Additional resection requires that the guide be reapplied, which may add time to the procedure unless one performs the subsequent resection by a freehand technique. Theoretically, the depth of the cutting guide should remove exactly the amount of bone replaced by the patella polyethylene component. However, this was not always the case in this investigation. Although we initially
Table 2 Comparison of Three Study Techniques.
Table 3 Comparison of Surgeon’s Preferred Techniques to New Techniques.
Asymmetry (SD) Difference from goal (SD) Time (SD)
Cutting Guide
Haptic
4 Quad
P Values
1.73 mm (1.04) 1.40 mm (1.04)
1.40 mm (0.88) 0.66 mm (0.64)
0.85 mm (0.73) 0.66 mm (0.59)
0.001* b0.001*
128 s (76.8)
102 s (34.7)
110 (62.5)
SD, standard deviation; mm, millimeters; s, seconds.
0.240
Discussion
Asymmetry (SD) Difference from goal (SD) Time (SD)
Surgeon’s Preferred Technique
Technique New to Surgeon
P Values
1.10 mm (0.62) 0.69 mm (0.61) 92 s (37.7)
1.44 mm (1.07) 1.01 mm (0.93) 124 s (67.5)
0.111 0.091 0.018*
SD, standard deviation; mm, millimeters; s, seconds.
C.L. Camp et al. / The Journal of Arthroplasty 30 (2015) 2110–2115
hypothesized that the guide would take the least amount of time to complete, there was no statistical difference seen amongst the three groups in regards to completion time. When comparing each surgeon’s preferred method to their performance with the other two methods that they were less experienced with, time to completion of the patellar resection was the only data point that achieved statistical significance with surgeons performing their preferred techniques more expediently. Although one would expect surgeon efficiency to improve with increasing repetitions of a new technique, based on this study alone, we are not able to confirm this. This study was not able to demonstrate significant difference between each surgeon’s preferred technique and the other two techniques regarding the outcomes of asymmetry and obtainment of resection goal. This suggests that resection accuracy is not solely determined by surgeon’s experience with a given technique. It should be noted though that although surgeons routinely perform their preferred technique in their practice, they were at least familiar with the other techniques prior to beginning the study. This may not be the case for all orthopedic surgeons. One of the main limitations of this study is the lack of long term follow up to identify measureable clinical outcome differences amongst patients in each study arm. Given the incidence of patellofemoral complications following TKA (b 7%), we would have needed to enroll more patients than we felt was practical to detect a significant differences in functional outcomes. Instead, the focus of this study was on the ability of surgeons to execute three distinct resection techniques in an accurate and timely manner. This study may be limited in that one of the techniques (freehand resection with four quadrant measurements) is designed to achieve the outcome used to assess all three techniques. This limitation could potentially be overcome if accurate measurements could be obtained radiographically. We were concerned that standard merchant view x-rays would not be precise enough for accurate measurements and that either in-growth series x-rays or CT scans would be required. We elected not to pursue these advanced imaging modalities in an attempt to contain costs and minimize unnecessary radiation exposure to patients. The main strength of this study is its prospective and randomized design with each surgeon’s historically preferred technique serving as their own internal control. It includes three experienced arthroplasty surgeons performing one of the most commonly performed operations in the US. To our knowledge, this study represents the first head to head comparison of multiple patellar resection techniques, and all techniques were completed in equal proportions by all participating surgeons. Additionally, an independent observer was utilized to make the final measurements used for statistical analysis to reduce measurement bias.
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Ultimately, use of a patellar cutting guide resulted in increased patellar asymmetry and decreased accuracy in obtaining desired patellar thickness compared to the other study techniques. It also required slightly more time to complete. When performing patellar resurfacing during TKA, care should be taken to ensure that precise bony resection is performed, especially when using a patellar cutting guide as this technique tends to produce a statistically less symmetric patellar resection than the free hand methods described in this study, although the clinical significance of this difference is yet to be determined. References 1. Barrack RL, Bertot AJ, Wolfe MW, et al. Patellar resurfacing in total knee arthroplasty. A prospective, randomized, double-blind study with five to seven years of follow-up. J Bone Joint Surg Am 2001;83-A(9):1376. 2. Burnett RS, Boone JL, McCarthy KP, et al. A prospective randomized clinical trial of patellar resurfacing and nonresurfacing in bilateral TKA. Clin Orthop Relat Res 2007; 464:65. 3. Burnett RS, Haydon CM, Rorabeck CH, et al. Patella resurfacing versus nonresurfacing in total knee arthroplasty: results of a randomized controlled clinical trial at a minimum of 10 years' follow-up. Clin Orthop Relat Res 2004(428):12. 4. Campbell DG, Duncan WW, Ashworth M, et al. Patellar resurfacing in total knee replacement: a ten-year randomised prospective trial. J Bone Joint Surg Br 2006; 88(6):734. 5. Schroeder-Boersch H, Scheller G, Fischer J, et al. Advantages of patellar resurfacing in total knee arthroplasty. Two-year results of a prospective randomized study. Arch Orthop Trauma Surg 1998;117(1-2):73. 6. Smith AJ, Wood DJ, Li MG. Total knee replacement with and without patellar resurfacing: a prospective, randomised trial using the profix total knee system. J Bone Joint Surg Br 2008;90(1):43. 7. Wood DJ, Smith AJ, Collopy D, et al. Patellar resurfacing in total knee arthroplasty: a prospective, randomized trial. J Bone Joint Surg Am 2002;84-A(2):187. 8. Rand JA. Patellar resurfacing in total knee arthroplasty. Clin Orthop Relat Res 1990(260):110. 9. Bindelglass DF, Cohen JL, Dorr LD. Patellar tilt and subluxation in total knee arthroplasty. Relationship to pain, fixation, and design. Clin Orthop Relat Res 1993(286):103. 10. Pagnano MW, Trousdale RT. Asymmetric patella resurfacing in total knee arthroplasty. Am J Knee Surg 2000;13(4):228. 11. Sneppen O, Gudmundsson GH, Bunger C. Patellofemoral function in total condylar knee arthroplasty. Int Orthop 1985;9(1):65. 12. Ranawat CS. The patellofemoral joint in total condylar knee arthroplasty. Pros and cons based on five- to ten-year follow-up observations. Clin Orthop Relat Res 1986(205):93. 13. Lombardi Jr AV, Mallory TH, Maitino PD, et al. Freehand resection of the patella in total knee arthroplasty referencing the attachments of the quadriceps tendon and patellar tendon. J Arthroplasty 1998;13(7):788. 14. Ledger M, Shakespeare D, Scaddan M. Accuracy of patellar resection in total knee replacement. A study using the medial pivot knee. Knee 2005;12(1):13. 15. Camp CL, Bryan AJ, Walker JA, et al. Surgical technique for symmetric patellar resurfacing during total knee arthroplasty. J Knee Surg 2013;26(4):281. 16. Schiavone Panni A, Cerciello S, Del Regno C, et al. Patellar resurfacing complications in total knee arthroplasty. Int Orthop 2014;38(2):313.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Resection Technique Does Affect Resection Symmetry and Thickness of the Patella During Total Knee Arthroplasty: A Prospective Randomized Trial Christopher L. Camp, MD , John R. Martin, MD, Aaron J. Krych, MD, Michael J. Taunton, MD, Luke Spencer-Gardner, MD, Robert T. Trousdale, MD Department of Orthopedic Surgery, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
a r t i c l e
i n f o
Article history: Received 27 March 2015 Accepted 21 May 2015 Keywords: total knee arthroplasty patellar resurfacing patellar resection knee arthritis patellofemoral joint
a b s t r a c t The purpose of this study was to evaluate the accuracy and efficiency of three patellar resection techniques: cutting guide, free hand with haptic feedback, and a novel technique utilizing four quadrant measurements. Ninety patients undergoing TKA were randomized to receive patellar resurfacing by one of the three study techniques. The novel four quadrant technique resulted in least post-resection asymmetry (0.85 mm, P = 0.001). The most accurate methods for obtaining desired thickness were haptic feedback (0.66 mm mean discrepancy [MD]) and novel four quadrant technique (0.66 mm MD) followed by the patellar cutting guide (1.40 mm MD) (P b 0.001). Use of a patellar cutting guide resulted in increased patellar asymmetry and decreased accuracy in obtaining desired patellar thickness in this prospective trial. © 2015 Elsevier Inc. All rights reserved.
Resurfacing of the patella during total knee arthroplasty (TKA) is a commonly performed procedure. Numerous randomized studies have attempted to determine the necessity of patellar resurfacing in the setting of a primary TKA [1–7]. These studies looked at factors believed to increase revision rates including: anterior knee pain, knee functional scores, patellar fractures, and patellar maltracking. Although a general consensus has not yet been reached on this topic, the majority of surgeons in the US routinely resurface the patella during primary TKA. Accordingly, a number of principles in patellar resection should be considered including: restoration of patellar height, performing symmetric resection, avoiding under-resection, and minimizing overstuffing of the patellofemoral joint [8]. The significance of this has been evaluated by examining complications associated with poor resection techniques such as 1) patellar fracture, 2) patellar maltracking, and 3) disruption of the extensor
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.05.038. Source of funding: Financial support for the statistical analysis and study coordination was obtained solely from internal funding. Level of Evidence: I. Prospective randomized controlled trial. Reprint requests: Christopher L. Camp, M.D., Mayo Clinic, 200 First St., SW, Rochester, MN, 55905. http://dx.doi.org/10.1016/j.arth.2015.05.038 0883-5403/© 2015 Elsevier Inc. All rights reserved.
mechanism [8–12]. Asymmetric resurfacing may lead to increased anterior knee pain, instability, and revision rates [10]. Due to these complications, a number of techniques have been described in an effort to optimize patient outcomes. Some advocate a haptic method, in which the surgeon estimates the patellar resection thickness and symmetry by feel while referencing anatomic landmarks such as the insertion sites of the quadriceps and patellar tendons [13]. The use of patellar resection cutting guides or jigs is another popular method utilized by many surgeons [14]. Recently, a novel freehand resection technique in which the posterior surface of the patella is divided into quadrants has been described [15]. Ring tipped calipers are utilized to determine the height of the remaining patella in each quadrant and the patella can then be accurately resected to the desired level based on these measurements. At our institution all three methods are routinely used for patellar resection. Patellar complications during TKA continue to be a problem affecting approximately 7% of patients undergoing primary TKA [16]. Although various studies have described individual results of patellar resections methods, none have attempted to compare the efficacy of various techniques in a head to head fashion. The following randomized prospective trial compares three commonly used patellar resection techniques: the use of a patellar cutting guide, haptic feedback, and the four quadrant technique. The main purpose of this study was to determine the most efficient method to symmetrically resurface the patella to the desired thickness during primary TKA. Additionally, this study assesses surgeon efficacy in patellar resection when learning a new technique as compared to their historically preferred method.
C.L. Camp et al. / The Journal of Arthroplasty 30 (2015) 2110–2115
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♦ ♦ ♦
Fig. 1. Flow chart illustrating patient enrollment.
Materials and Methods After approval from our institution’s internal review board and our department’s orthopedic research review committee, a total of 90 patients undergoing TKA were prospectively enrolled into this randomized controlled trial (registered at www.clinicaltrials.gov) prior to surgery (Fig. 1). To be considered for the study, patients had to meet the following inclusion criteria: undergoing elective primary TKA with patellar resurfacing, willing to participate, and able to provide informed consent. Patients were excluded if they were undergoing revision TKA, were not definitively having their patella resurfaced at the time of TKA, or were unable or unwilling to provide informed consent. All surgeries were performed by one of three experienced arthroplasty surgeons (AJK, MJT, and RTT) who each enrolled a total of 30 patients (total n = 90). Within each of these three subgroups (A, B, and C) of 30 patients, patients were equally randomized to have their patella resected by one of the following three techniques during TKA: 1) use of a standard cutting guide, 2) freehand resection with haptic feedback or 3) freehand resection guided by four quadrant measurements. A total of 10 patients per surgeon were randomized to each technique. This resulted in 30 patients randomized to each technique across all surgeons (Table 1). Each of the three surgeons was familiar with all three resection techniques; however, they each preferred one of the techniques over the other two and historically performed the vast majority of their patellar resections in that manner. Prior to the study, no two surgeons preferred the same technique (Table 1). As a result, each surgeon was more
experienced with their own preferred resection method, but they had at least used the other two techniques previously. Informed consent was obtained from all patients in the clinical setting during their pre-surgical appointment. Randomization was completed by envelope system by an independent member of the study team that did not participate in the surgery or data collection (CLC). Each surgeon was provided with 30 sequentially numbered envelopes (1 through 30) that each contained a single data collection sheet. Surgeons were not allowed to open the envelopes until they were in the operating room. The technique to be performed was indicated on the data sheet in addition to the outcome measures. All procedures were performed entirely by the staff surgeons and they were timed from
Table 1 Patient Allocation. Cutting Guide Resections Performed by Surgeon A Resections Performed by Surgeon B Resections Performed by Surgeon C
10
a
Haptic Feedback 10
10
10
10
10
4 Quadrant 10
a
10 10a
A total of ninety patients were enrolled. There were thirty patients per surgeon and thirty patients per technique. a Indicates the surgeon’s historically preferred technique.
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C.L. Camp et al. / The Journal of Arthroplasty 30 (2015) 2110–2115
who completed the resection. This was not timed. The difference between the thickest and the thinnest measurements was reported as the value of asymmetry. Ability to obtain resection goal was calculated by taking the difference between the surgeon’s previously stated goal and the average thickness of the four quadrants measured by the resident or fellow. If so inclined, the surgeon was allowed to revise the resection as needed using any technique of their choosing after all final study measurements were made by the resident or fellow. Standard onlay type patellar prostheses were used in all patients. Descriptions of Techniques
Fig. 2. Four quadrant method for assessing patellar resection symmetry and thickness.
start (first measurement of native patellar thickness) to finish (final measurement of resected patella). Outcome measures included patient demographic data such as age, gender, operative side, surgical indication for TKA, and implant type. Intraoperative outcome measures included: pre-resection thickness, goal for post-resection thickness, symmetry of resection, obtainment of resection goal, and time to complete the resection. Medial parapatellar arthrotomies were used for all patients. Each patellar resection procedure began by exposing the articular surface of the patella. Once the patella was fully exposed and the surgeon measured native patellar thickness, the timer was started. The surgeon would subsequently state their goal for post resection thickness (typically the thickness of the implant), and these values were recorded. The resection was performed according to randomized study technique. After the final resection, the timer was stopped. Post-resection symmetry of the patella was independently assessed by a resident or fellow who was not involved in the resection. This was evaluated by dividing the patella into four equal quadrants and measuring the thickness in the center of each quadrant using a ring tipped or “C” shaped caliper (Fig. 2) [15]. To reduce bias, post resection assessment was not performed by the staff surgeon
Standard Cutting Guide The native patellar thickness was measured using flat tipped calipers (Fig. 3A) and the goal for post resection thickness was noted. The cutting guide was set to the desired resection depth and applied in a symmetric fashion using the articular surface, anterior surface, and the insertion points of the quadriceps and patellar tendons for reference (Fig. 3B). The resection was made through the slot of the guide with a saw (Fig. 3C). The guide was removed, but surgeons were permitted to reapply the guide to recut the patella if they felt that additional resection was required. The patellar trial was placed and the restored thickness was measured (Fig. 3D). Freehand Resection, Haptic Feedback Native thickness was measured (Fig. 4A), and post resection goal was stated. The patella was resected in a freehand manner with an oscillating saw (Fig. 4B), and the surgeon judged symmetry based on haptic feedback (Fig. 4C) and thickness by measuring the anterior to posterior distance in the center of the patella. The resection was repeated as necessary until the desired thickness and symmetry were obtained. The patellar trial was placed and overall thickness was measured (Fig. 4D) [13]. Freehand Resection, Four Quadrant Measurements Native patellar thickness was measured (Fig. 5A). Post resection thickness goal was stated, and the resection was performed freehand (Fig. 5B) using an oscillating saw and anatomic landmarks as a guide. The patella was divided into four quadrants and thickness was
Fig. 3. Standard cutting guide technique. The native patellar height is measured (A). The guide is applied (B) and the resection performed (C). Final height is measured with the prosthesis in place (D).
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Fig. 4. Freehand resection haptic feedback technique. The native patellar height is measured (A). Freehand resection is performed (B) and the symmetry and height are assessed using haptic feedback (C). Final height is measured with the prosthesis in place (D).
measured in the center of each quadrant using ring tipped or “C” shaped caliper (Fig. 5C). Resection was repeated based on these four measurements as needed until satisfactory symmetry and resection were obtained. The patellar button was placed and overall thickness was assessed (Fig. 5D) [15]. Statistical Analysis Prior to enrollment, an a priori power analysis was conducted using radiographic data from postoperative merchant view x-rays on a
historical sample of 29 subjects who had previously undergone TKA with patellar resurfacing. In this cohort, patellar thickness was measured radiographically at the central border of the medial and lateral quartiles of the patella (Fig. 6). The mean discrepancy between these measures was 1.1 mm (standard deviation 0.68 mm). Assuming that similar variability would be observed in this study, a sample of 30 subjects per each of the three study groups (90 total) would provide 90% power to detect a difference in means between any two of the three groups of at least 0.6 mm (α = 0.05, two-sided test). Although postoperative merchant view x-rays may not provide equivalent accuracy
Fig. 5. Freehand resection quadrant measurement technique. The native patellar height is measured (A). Freehand resection is performed (B) and the symmetry and height are assessed in the center of all four quadrants of the resected surface (C). Final height is measured with the prosthesis in place (D).
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Fig. 6. Comparison of discrepancy in asymmetry and difference from goal for each technique.
compared to intra-operative measurement of patellar thickness, it was felt that it would be a reasonable surrogate for power analysis. Statistical analysis focused on: time to complete the procedures, discrepancy between the largest and smallest thickness measurements from the four quadrants of the resurfaced patella, and the discrepancy between mean post resection thickness and surgeon goal. Data are presented as means with ranges and standard deviations (SD) where appropriate. Since these differences represented means of normally distributed continuous variables, an analysis of variance (ANOVA) was used when comparing the three study techniques and a student t test was used when comparing surgeons’ historically preferred methods to the techniques that they were less experienced with. All statistical tests were two-sided and P values less than 0.05 were considered statistically significant.
they were less familiar with. Surgeon A historically preferred technique 1 (cutting guide); Surgeon B preferred technique 2 (haptic feedback); and Surgeon C preferred technique 3 (four quadrant). The 30 patients that underwent resection by their surgeon’s historically preferred technique made up one group and the other group was composed of the 60 patients who received patellar resurfacing by a technique that their surgeon was less experienced with (Table 3). No statistically significant differences were noted in patellar asymmetry (1.10 [SD 0.62] versus 1.44 [SD 1.07] mm; p = 0.111) or obtainment of surgeon goal (0.69 [SD 0.61] versus 1.01 [SD 0.93]; p = 0.091; Table 3). Surgeons were able to execute their preferred techniques in less time than the new techniques (92 [SD 37.8] versus 124 [SD 67.5] s; p = 0.018).
Results The three senior authors each performed 30 patellar resurfacings during primary TKA on a total of 90 patients over a 12 month period. There were 42 males and 48 females in the cohort with a mean age of 67.6 years (range, 42–86 years). The surgical diagnosis was osteoarthritis in all patients and 41 surgeries were right sided while 49 were left. Each surgeon performed each of the three study techniques a total of 10 times. The mean asymmetry for Group One (standard cutting guide) was 1.73 mm (range 0–4 mm; SD 1.04) while Group Two (Haptic Feedback) was 1.40 mm (range 0–3 mm; SD 0.88) and Group Three (Four Quadrant) was 0.85 mm (range 0–2 mm; SD 0.73) (Table 2). The four quadrant technique was found to most accurately produce symmetric patellar resections (p = 0.001) (Fig. 6). The difference between surgeon goal and actual resection height for each method was: cutting guide 1.40 mm (range 0–4.5 mm; SD 1.04), haptic feedback 0.66 mm (range 0–2.25 mm; SD 0.64) and four quadrant method 0.66 mm (range 0–2 mm; SD 0.59)(p b 0.001; Table 2). Each procedure was timed from the first measurement of native thickness made by the surgeon to the completion of their last resection. The time values did not differ significantly for the three techniques (p = 0.240; Table 3): cutting guide 128 s (range 22–311 s; SD 76.8), haptic feedback 102 s (range 48–180 s; SD 34.7), and four quadrant 110 s (range 40–280 s; SD 62.5) (Fig. 6). Surgeons’ performance utilizing their historically preferred technique was compared to their performance on the two techniques that
Patellar complications resulting from poor technique (fracture, extensor mechanism disruption, and maltracking) are not uncommon following TKA with a reported incidence of 7% [9,10,16]. In an effort to minimize these complications, attention should be directed towards optimizing resection symmetry, avoiding over or under resection, and resurfacing the patella in a timely manner. The current study is the first randomized prospective trial to evaluate three techniques commonly used for patellar resurfacing in an attempt to determine the most efficient manner to create a symmetrically resected patella of the appropriate thickness. Of the techniques studied, the four quadrant technique produced the most accurate patellar resections. Achieving the intraoperative goal for patellar thickness was most reproducible with the haptic feedback and four quadrant techniques compared to the standard cutting guide. These freehand techniques allow frequent and easy assessment of thickness and symmetry during the resection process. The cutting guide has the benefit of producing a smooth and even cut when cutting through the slot; however, it is dependent on the surgeon’s ability to apply the guide at the appropriate depth and obliquity. Another limitation of the guide is that it is difficult to fully evaluate the effectiveness of the resection without removing it. Additional resection requires that the guide be reapplied, which may add time to the procedure unless one performs the subsequent resection by a freehand technique. Theoretically, the depth of the cutting guide should remove exactly the amount of bone replaced by the patella polyethylene component. However, this was not always the case in this investigation. Although we initially
Table 2 Comparison of Three Study Techniques.
Table 3 Comparison of Surgeon’s Preferred Techniques to New Techniques.
Asymmetry (SD) Difference from goal (SD) Time (SD)
Cutting Guide
Haptic
4 Quad
P Values
1.73 mm (1.04) 1.40 mm (1.04)
1.40 mm (0.88) 0.66 mm (0.64)
0.85 mm (0.73) 0.66 mm (0.59)
0.001* b0.001*
128 s (76.8)
102 s (34.7)
110 (62.5)
SD, standard deviation; mm, millimeters; s, seconds.
0.240
Discussion
Asymmetry (SD) Difference from goal (SD) Time (SD)
Surgeon’s Preferred Technique
Technique New to Surgeon
P Values
1.10 mm (0.62) 0.69 mm (0.61) 92 s (37.7)
1.44 mm (1.07) 1.01 mm (0.93) 124 s (67.5)
0.111 0.091 0.018*
SD, standard deviation; mm, millimeters; s, seconds.
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hypothesized that the guide would take the least amount of time to complete, there was no statistical difference seen amongst the three groups in regards to completion time. When comparing each surgeon’s preferred method to their performance with the other two methods that they were less experienced with, time to completion of the patellar resection was the only data point that achieved statistical significance with surgeons performing their preferred techniques more expediently. Although one would expect surgeon efficiency to improve with increasing repetitions of a new technique, based on this study alone, we are not able to confirm this. This study was not able to demonstrate significant difference between each surgeon’s preferred technique and the other two techniques regarding the outcomes of asymmetry and obtainment of resection goal. This suggests that resection accuracy is not solely determined by surgeon’s experience with a given technique. It should be noted though that although surgeons routinely perform their preferred technique in their practice, they were at least familiar with the other techniques prior to beginning the study. This may not be the case for all orthopedic surgeons. One of the main limitations of this study is the lack of long term follow up to identify measureable clinical outcome differences amongst patients in each study arm. Given the incidence of patellofemoral complications following TKA (b 7%), we would have needed to enroll more patients than we felt was practical to detect a significant differences in functional outcomes. Instead, the focus of this study was on the ability of surgeons to execute three distinct resection techniques in an accurate and timely manner. This study may be limited in that one of the techniques (freehand resection with four quadrant measurements) is designed to achieve the outcome used to assess all three techniques. This limitation could potentially be overcome if accurate measurements could be obtained radiographically. We were concerned that standard merchant view x-rays would not be precise enough for accurate measurements and that either in-growth series x-rays or CT scans would be required. We elected not to pursue these advanced imaging modalities in an attempt to contain costs and minimize unnecessary radiation exposure to patients. The main strength of this study is its prospective and randomized design with each surgeon’s historically preferred technique serving as their own internal control. It includes three experienced arthroplasty surgeons performing one of the most commonly performed operations in the US. To our knowledge, this study represents the first head to head comparison of multiple patellar resection techniques, and all techniques were completed in equal proportions by all participating surgeons. Additionally, an independent observer was utilized to make the final measurements used for statistical analysis to reduce measurement bias.
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Ultimately, use of a patellar cutting guide resulted in increased patellar asymmetry and decreased accuracy in obtaining desired patellar thickness compared to the other study techniques. It also required slightly more time to complete. When performing patellar resurfacing during TKA, care should be taken to ensure that precise bony resection is performed, especially when using a patellar cutting guide as this technique tends to produce a statistically less symmetric patellar resection than the free hand methods described in this study, although the clinical significance of this difference is yet to be determined. References 1. Barrack RL, Bertot AJ, Wolfe MW, et al. Patellar resurfacing in total knee arthroplasty. A prospective, randomized, double-blind study with five to seven years of follow-up. J Bone Joint Surg Am 2001;83-A(9):1376. 2. Burnett RS, Boone JL, McCarthy KP, et al. A prospective randomized clinical trial of patellar resurfacing and nonresurfacing in bilateral TKA. Clin Orthop Relat Res 2007; 464:65. 3. Burnett RS, Haydon CM, Rorabeck CH, et al. Patella resurfacing versus nonresurfacing in total knee arthroplasty: results of a randomized controlled clinical trial at a minimum of 10 years' follow-up. Clin Orthop Relat Res 2004(428):12. 4. Campbell DG, Duncan WW, Ashworth M, et al. Patellar resurfacing in total knee replacement: a ten-year randomised prospective trial. J Bone Joint Surg Br 2006; 88(6):734. 5. Schroeder-Boersch H, Scheller G, Fischer J, et al. Advantages of patellar resurfacing in total knee arthroplasty. Two-year results of a prospective randomized study. Arch Orthop Trauma Surg 1998;117(1-2):73. 6. Smith AJ, Wood DJ, Li MG. Total knee replacement with and without patellar resurfacing: a prospective, randomised trial using the profix total knee system. J Bone Joint Surg Br 2008;90(1):43. 7. Wood DJ, Smith AJ, Collopy D, et al. Patellar resurfacing in total knee arthroplasty: a prospective, randomized trial. J Bone Joint Surg Am 2002;84-A(2):187. 8. Rand JA. Patellar resurfacing in total knee arthroplasty. Clin Orthop Relat Res 1990(260):110. 9. Bindelglass DF, Cohen JL, Dorr LD. Patellar tilt and subluxation in total knee arthroplasty. Relationship to pain, fixation, and design. Clin Orthop Relat Res 1993(286):103. 10. Pagnano MW, Trousdale RT. Asymmetric patella resurfacing in total knee arthroplasty. Am J Knee Surg 2000;13(4):228. 11. Sneppen O, Gudmundsson GH, Bunger C. Patellofemoral function in total condylar knee arthroplasty. Int Orthop 1985;9(1):65. 12. Ranawat CS. The patellofemoral joint in total condylar knee arthroplasty. Pros and cons based on five- to ten-year follow-up observations. Clin Orthop Relat Res 1986(205):93. 13. Lombardi Jr AV, Mallory TH, Maitino PD, et al. Freehand resection of the patella in total knee arthroplasty referencing the attachments of the quadriceps tendon and patellar tendon. J Arthroplasty 1998;13(7):788. 14. Ledger M, Shakespeare D, Scaddan M. Accuracy of patellar resection in total knee replacement. A study using the medial pivot knee. Knee 2005;12(1):13. 15. Camp CL, Bryan AJ, Walker JA, et al. Surgical technique for symmetric patellar resurfacing during total knee arthroplasty. J Knee Surg 2013;26(4):281. 16. Schiavone Panni A, Cerciello S, Del Regno C, et al. Patellar resurfacing complications in total knee arthroplasty. Int Orthop 2014;38(2):313.
