Serial Changes in Knee Muscle Strength After Anterior Cruciate Ligament Reconstruction Using Hamstring Tendon Autografts Dae-Hee Lee, M.D., Jin-Hyuck Lee, P.T., Hye-Jin Jeong, P.T., and Seok-Joo Lee, P.T.
Purpose: The purpose of this study was to evaluate serial changes in quadriceps and hamstring muscle strength over the first postoperative year in patients who underwent anterior cruciate ligament (ACL) reconstruction with an autologous hamstring tendon graft and to reveal which of these 2 muscles lost more strength and recovered more slowly after autologous hamstring ACL reconstruction. Methods: Isokinetic muscle strength was measured preoperatively and at 6 months and 1 year postoperatively in 20 patients who underwent ACL reconstruction. The maximal torque (60 /s) and total work (180 /s) of the quadriceps and hamstring were evaluated using an isokinetic testing device. The isokinetic muscle strength and endurance of the injured legs were expressed as percentages of those of the uninjured legs at the same time point. Results: Both quadriceps and hamstring muscle strength at 60 /s and endurance at 180 /s of the injured relative to the uninjured leg was 50% preoperatively. Quadriceps muscle strength and endurance of the injured leg increased to 70% at 6 months and 80% at 1 year postoperatively, whereas hamstring muscle strength and endurance increased to 80% at 6 months and 80% at 1 year. Conclusions: Knee muscle strength recovered progressively after ACL reconstruction using autologous hamstring tendons but did not fully recover, being about 80% that of the uninjured leg even 1 year after surgery. Level of Evidence: Level IV, therapeutic case series.
T
he clinical outcomes of anterior cruciate ligament (ACL) reconstruction include recovery of muscle strength1,2 as well as the knee regaining good stability and sufficient range of motion.3,4 Despite the advantages of satisfactory tensile graft strength and tunnel fixation resulting from fast and strong bone-to-bone tunnel healing,5-7 the use of autologous boneepatellar tendonebone grafts has rapidly diminished because of
From the Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine (D-H.L), Seoul; and Sports Medical Center (J-H.L., H-J.J., S-J.L.), Korea University College of Medicine, Anam Hospital, Seoul, Republic of Korea. The authors report the following potential conflict of interest or source of funding: This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF2013R1A1A2A10010605), funded by the Ministry of Education, Science and Technology. This work was also supported by Korea University grant K1423281. Received May 1, 2014; accepted December 3, 2014. Address correspondence to Dae-Hee Lee, M.D., Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 135-710, Republic of Korea. E-mail: [email protected] Ó 2015 by the Arthroscopy Association of North America 0749-8063/14380/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.12.005
donor site morbidity, including anterior knee pain and patellar fracture,8-11 and long-term quadriceps femoris dysfunction even after 9 years.12 this has increased the use of quadruple hamstring tendons as a graft source. Use of a boneepatellar tendonebone autograft results in a postoperative decrease in knee extension strength13-15 followed by recovery over time, although losses of hamstring strength are minimal using this technique.16 In contrast, during hamstring autograft ACL reconstruction, loss of muscle strength after surgery is likely to be greater in the knee flexor than in the extensor because of harvesting of the hamstring tendon, although it has not yet been determined whether extensor (quadriceps) muscle strength decreases more than flexor (hamstring) muscle strength.17 In addition, the patterns of postoperative recovery of muscle strength from preoperative levels are also not clearly understood in patients who undergo autologous hamstring graft ACL reconstruction, because of a lack of data on preoperative muscle strength in previous studies. The purpose of this study was to evaluate serial changes over the first postoperative year in quadriceps and hamstring muscle strength in patients who underwent ACL reconstruction with an autologous
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hamstring tendon graft and to reveal which of these 2 muscles lost more strength and recovered more slowly after autologous hamstring ACL reconstruction. It was hypothesized that in patients who undergo autologous hamstring tendon graft ACL reconstruction, isokinetic knee muscle strength would recover progressively after surgery but would not recover fully, even after 1 year, and that the recovery of the knee flexor (hamstring) would be more delayed than that of the knee extensor (quadriceps) because hamstring harvesting would result in a greater deficit of hamstring than of quadriceps muscle strength.
Methods Study Design and Patient Enrollment This prospective longitudinal trial enrolled patients who were candidates for ACL reconstruction with 4-stranded hamstring autografts (gracilis plus semitendinosus) between 2011 and 2012. Patients were included only if they had unilateral isolated ACL rupture as confirmed by magnetic resonance imaging and physical examinations such as positive anterior draw, Lachman, and pivot shift tests (more than grade II), or a combination of examinations. Patients with ACL tears associated with meniscus tears were excluded to eliminate the bias resulting from meniscus tears. Also, patients with bilateral ACL injuries or concomitant injuries to any other ligament (i.e., the medial or lateral collateral ligament or the posterior cruciate ligament) or any associated extra-articular lesions were excluded. Patients were also excluded if they were unable to perform the isokinetic muscle strength test because of pain (usually caused by limited motion of the knee joint) resulting from an inadequate interval from injury (< 4 weeks). No nerve block was used at the time of surgery. Of the 27 patients (27 knees) approached, 25 agreed to take part in the study. After assessing for eligibility, 23 patients were enrolled. The final analysis involved data from 20 patients because 3 patients did not undergo complete isokinetic strength tests at the 3 time points (preoperatively and at 6 months and 1 year postoperatively). The baseline demographic characteristics of the participants are described in Table 1. The study protocol was approved by our institutional review board, and all participants provided written informed consent before participation.
Assessment of Isokinetic Strength All patients performed isokinetic muscle strength tests preoperatively and 6 months and 1 year postoperatively using a Biodex Multi-Joint System 4 (Biodex Medical Systems, Shirley, NY). The participants sat in an upright position on the dynamometer chair with a strap across the chest; they grasped the edge of the bench and flexed their hips and knees 90 each (Fig 1). The range of motion of the tested knee joint was set from full extension (0 ) to 100 flexion. Testing consisted of maximal concentric quadriceps/concentric hamstring reciprocal contractionsd5 at an angular velocity of 60 /s and 15 at 180 /sdwith a rest time of 30 seconds between tests. Before each test session, patients performed 5 warmup knee flexions and extensions for each leg at 60 /s. Peak torque, defined as the single highest point in the torque curve (N$m) of flexion and extension at 60 /s, was evaluated to determine muscle strength. Total work, defined as the sum total of the area under all torque
Table 1. Demographic Characteristics of Study Participants Number of male to female patients Age, yr (range) Height, cm (range) Weight, kg (range) Body mass index, kg/m2 (range) Time interval from injury to testing, mo (range)
15:5 30.5 (17-51) 170.1 (152-183) 73.3 (48-130) 25.8 (19.2-40.1) 5.1 5.3 (2-26)
Fig 1. Measurement of isokinetic muscle strength using a dynamometer.
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curves in the test repetitions (J) of flexion and extension at 180 /s, was evaluated to determine muscular endurance, defined as the ability of the muscles to perform repeated contractions against a load.18,19 Extensor strength and endurance were regarded as quadriceps strength and endurance, respectively, and flexor strength and endurance were regarded as hamstring strength and endurance, respectively. Especially when evaluating hamstring strength, an additional measurement of flexion torque at 90 was obtained from the torque curves recorded at 60 /s. This enabled an accurate evaluation of the recovery of hamstring strength at deep knee flexion, because insufficient hamstring muscle strength in deep knee flexion after ACL reconstruction with a hamstring tendon autograft has been reported.20,21 Two trials of each were performed, with their mean set as maximal peak torque and total work of the hamstring and quadriceps muscles. To analyze the recovery of muscle strength and endurance in the operated leg, the isokinetic muscle strength and endurance of this leg were expressed as percentages of those of the unoperated leg of the same patient at the same time point. Statistical Analysis A priori power analysis was performed to determine the sample size using the 2-sided hypothesis test at an alpha level of 0.05 and a power of 0.8. A pilot study of 5 knees found that the standard deviations for preoperative and 6-month postoperative isokinetic maximal torques of the quadriceps were 10% and 12%, respectively. We calculated that 17 knees were required to detect a 20% difference in the isokinetic maximal torque of the quadriceps from before surgery to 6 months after surgery, assuming the standard deviations taken from a pilot study of 5 knees. The current study finally involved 20 patients, indicating adequate power (0.885) for detecting a significant difference between the 2 evaluations.
Repeated-measures analysis of variance was used to evaluate changes in isokinetic muscle strength over time. This method takes into account outcome measurements over time and correlates successive outcomes. Post hoc Tukey tests were used to determine which 2 of the 3 time points differed significantly. All statistical analyses were performed using IBM SPSS Statistics, version 20 (SPSS, Chicago, IL). P < .05 was considered statistically significant.
Results
The peak torque at 60 /s and the total work at 180 /s of the quadriceps and hamstring muscles of both the involved and uninvolved limbs were higher 6 months and 1 year after than before ACL reconstruction. However, the hamstring to quadriceps ratios of both the involved and uninvolved limbs were similar before and after surgery (Table 2). The isokinetic maximal peak torques at 60 /s and endurance at 180 /s of the quadriceps and hamstring were significantly lower on the involved than on the uninvolved sides at all 3 time points. The quadriceps and hamstring maximal peak torques of the uninvolved leg versus the involved leg at 60 /s were, respectively, 185 versus 93 N$m (P < .001) and 90 versus 44 N$m (P < .001) preoperatively, 216 versus 153 N$m (P ¼ .003) and 112 versus 88 N$m (P < .001) at 6 months postoperatively, and 228 versus 178 N$m (P < .001) and 119 versus 93 N$m (P < .001) at 1 year postoperatively (Fig 2 A and B). The quadriceps and hamstring endurance of the uninvolved leg versus the involved leg at 180 /s were, respectively, 1,479 versus 742 J (P < .001) and 850 versus 363 J (P < .001) preoperatively, 1,608 versus 1,124 J (P < .001) and 945 versus 775 J (P ¼ .009) at 6 months postoperatively, and 1,681 versus 1,393 J (P < .001) and 1,042 versus 871 J (P < .001) at 1 year postoperatively (Fig 2 C and D). The quadriceps muscle strength at 60 /s and endurance at 180 /s of the injured leg compared with the uninjured leg increased significantly, being 50%
Table 2. Serial Changes in Muscle Strength and Hamstring to Quadriceps Ratios of Participants Who Underwent Anterior Cruciate Ligament Reconstruction Variable Quadriceps 60 , uninvolved leg, N$m Quadriceps 60 , involved leg, N$m Hamstring 60 , uninvolved leg, N$m Hamstring 60 , involved leg, N$m Hamstring to quadriceps ratio 60 , uninvolved leg Hamstring to quadriceps ratio 60 , involved leg Quadriceps 180 , uninvolved leg, J Quadriceps 180 , involved leg, J Hamstring 180 , uninvolved leg, J Hamstring 180 , involved leg, J Hamstring to quadriceps ratio 180 , uninvolved leg Hamstring to quadriceps ratio 180 , involved leg
Preoperative Status 185 47 93 51 90 31 44 31 52% 15% 64% 33% 1,479 456 742 432 850 346 363 309 58% 10% 60% 17%
NOTE. Data are expressed as mean SD unless otherwise indicated.
6 Mo Postoperatively 216 72 153 65 112 33 88 24 48% 9% 65% 18% 1,608 521 1,124 481 945 390 775 298 59% 12% 72% 16%
1 Yr Postoperatively 228 72 178 69 119 42 96 41 51% 7% 59% 13% 1,681 533 1,393 504 1,042 346 871 304 57% 15% 63% 13%
P Value .022 < .001 .009 < .001 .25 .23 .08 < .001 .028 < .001 .96 .09
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Fig 2. Isokinetic muscle strength and endurance on the involved and uninvolved sides in patients who underwent autologous hamstring anterior cruciate ligament (ACL) reconstruction preoperatively and 6 months and 1 year postoperatively. Maximal peak torques of the (A) quadriceps and (B) hamstring muscles at 60 /s. Total work of the (C) quadriceps and (D) hamstring muscles at 180 /s. (EX, extension; FL, flexion.)
preoperatively, 70% after 6 months, and 80% after 1 year. The hamstring muscle strength at 60 /s and endurance at 180 /s of the injured leg compared with the uninjured leg also increased significantly but with a slightly different pattern, being 50% preoperatively, 80% at 6 months, and 80% at 1 year. This recovery pattern of hamstring muscle strength was also seen at deep knee flexion of 100 (Table 3). The mean percentage quadriceps muscle strength and endurance of the injured leg compared with the uninjured leg increased significantly not only from before to 6 months after surgery but also between 6 months and 1 year postoperatively (Fig 3 A and B). In contrast, the mean percentage hamstring muscle strength and endurance of the injured leg compared with the uninjured leg increased significantly only from before surgery to 6 months after surgery but not from 6 months to 1 year (Fig 3 C and D). Compared with preoperative measurements of the uninjured knee, the mean quadriceps muscle strength of the injured knee at 60 /s was 81% 6 months after surgery and 94% after 1 year, whereas the quadriceps muscle endurance of the injured knee at 180 /s was 77% after
6 months and 95% after 1 year. In contrast, the mean hamstring muscle strength at 60 /s on the injured side was 170% after 6 months and 190% after 1 year compared with the preoperative hamstring muscle strength on the uninjured side, whereas the hamstring endurance at 180 /s on the injured side recovered to 97% after 6 months and to 113% after 1 year.
Discussion The most important finding of the present study was that isokinetic knee muscle strength recovered progressively after hamstring-harvested ACL reconstruction but did not recover fully even 1 year after surgery. In addition, the results showed that hamstring strength recovered faster than quadriceps strength, despite harvesting of the autologous hamstring. Losses in quadriceps strength have been reported to be approximately 10% greater than losses in hamstring strength after ACL reconstruction using autologous patellar tendon grafts.22 In patients undergoing ACL reconstruction with autologous hamstring grafts, we hypothesized that because of hamstring harvesting, knee flexion (hamstring) strength would be more
Table 3. Serial Changes in Muscle Strength and Endurance Expressed as the Percentage of Injured to Uninjured Limb Before and After Surgery Variable Quadriceps 60 percentage, involved/uninvolved legs 100, % Hamstring 60 percentage, involved/uninvolved legs 100, % Quadriceps 180 percentage, involved/uninvolved legs 100, % Quadriceps 180 percentage, involved/uninvolved legs 100, % Hamstring percentage, 100 flexion, involved/uninvolved legs 100, % NOTE. Data are expressed as mean SD unless otherwise indicated.
Preoperative Status 49 22 49 37 51 26 51 40 51 37
6 Mo Postoperatively 66 21 79 14 71 22 80 19 77 30
1 Yr Postoperatively 78 23 80 24 84 17 85 13 82 27
P Value .002 .001 .001 .018 < .001
KNEE MUSCLE STRENGTH AFTER ACL RECONSTRUCTION
Fig 3. Serial changes in muscle strength and endurance percentages of the (A and B) quadriceps and (C and D) hamstring muscles of the injured leg compared with the uninjured leg.
decreased postoperatively than knee extension (quadriceps) strength. Contrary to our hypothesis, however, we observed a greater loss in quadriceps muscle strength than in hamstring muscle strength after 1 year in 20 patients who underwent quadruple hamstring tendon ACL reconstruction. These results were consistent with the Eriksson et al.21 study evaluating 16 autologous hamstring ACL reconstructions, which found that the deficit in quadriceps strength was greater than the deficit in hamstring strength after a minimum of 6 months.21 The reason for the better recovery of hamstring than quadriceps strength is unclear but may result from the greater reduction in quadriceps than hamstring muscle volume after ACL reconstruction, with the former decreasing about 10%. In addition, the neotendon that regenerates at the site of the hamstring tendon could reduce and compensate for losses in hamstring muscle strength caused by hamstring harvesting.21,23 Previous studies24,25 have shown greater losses in quadriceps than hamstring strength after ACL reconstruction with autologous patellar tendons, along with slower recovery of quadriceps strength than hamstring strength. A study of serial changes in muscle performance in patients who underwent autologous patellar tendon ACL reconstruction showed that postoperative quadriceps strength on the injured side was approximately 60% after 6 months, 70% after 1 year, and 90% after 2 years compared with the uninjured side.3 In contrast, the hamstring strength of the operated leg was about 90% to 95% that of the contralateral leg after 6 months, with this strength maintained thereafter. To our knowledge, only one previous study has assessed changes over time in isokinetic knee muscle strength from before to after ACL reconstruction with autologous hamstring tendons. A study of 31 participants found that the mean preoperative quadriceps and hamstring strength of the injured leg was 93% and nearly 100%, respectively, that of the uninjured leg
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because of a 6- to 8-week preoperative physiotherapy program.26 Postoperative quadriceps and hamstring strength of the injured leg 6 months after surgery decreased to about 90% that of the uninjured leg, suggesting that recovery of hamstring strength was slower than that of quadriceps strength because of hamstring harvest for ACL grafts. However, the followup period (6 months) of that study was too short to show progressive recovery patterns of muscle strength after ACL reconstruction. In contrast to previous results,26 we found that recovery of isokinetic quadriceps performance was slower than that of hamstring performance, even when the graft was harvested from the hamstring. However, caution should be exercised in comparing the results of these studies because of differences in the time interval from injury to surgery and pre- and postoperative rehabilitation protocols. Limitations This study had several limitations. One of the most important limitations was the lack of a healthy control group. However, it is very difficult to select control participants with the same activity level or athletic history as participants with ACL tears. Rather, data from the uninvolved side were used as a control for the involved side. However, bilateral muscle strength impairment was possible, suggesting that aberrant afferent information in the intra-articular receptors in the injured limb may also affect muscle strength in the contralateral uninjured limb.27 Another limitation was that we did not assess the relationships between serial changes in muscle strength and clinical outcomes; however, that was not the primary aim of this study. Finally, the isokinetic muscle strength and endurance measured in this study may be insufficient to reflect patients’ activities of daily life, including physical labor and participation in sports.
Conclusions Knee muscle strength recovered progressively after ACL reconstruction using autologous hamstring tendons but did not fully recover, being about 80% that of the uninjured leg even 1 year after surgery.
References 1. de Jong SN, van Caspel DR, van Haeff MJ, Saris DB. Functional assessment and muscle strength before and after reconstruction of chronic anterior cruciate ligament lesions. Arthroscopy 2007;23:21-28:28.e1-28.e3. 2. Eitzen I, Holm I, Risberg M. Preoperative quadriceps strength is a significant predictor of knee function two years after anterior cruciate ligament reconstruction. Br J Sports Med 2009;43:371-376. 3. Kobayashi A, Higuchi H, Terauchi M, Kobayashi F, Kimura M, Takagishi K. Muscle performance after anterior cruciate ligament reconstruction. Int Orthop 2004;28: 48-51.
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4. Kim HS, Seon JK, Jo AR. Current trends in anterior cruciate ligament reconstruction. Knee Surg Relat Res 2013;25: 165-173. 5. Engebretsen L, Benum P, Fasting O, Mølster A, Strand T. A prospective, randomized study of three surgical techniques for treatment of acute ruptures of the anterior cruciate ligament. Am J Sports Med 1990;18: 585-590. 6. Noyes F, Butler D, Grood E, Zernicke R, Hefzy M. Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions. J Bone Joint Surg Am 1984;66:344-352. 7. Koh HS, In Y, Kong CG, Won HY, Kim KH, Lee JH. Factors affecting patients’ graft choice in anterior cruciate ligament reconstruction. Clin Orthop Surg 2010;2: 69-75. 8. Miller LCMD, Nichols T, Butler LCCA. Patella fracture and proximal patellar tendon rupture following arthroscopic anterior cruciate ligament reconstruction. Arthroscopy 1999;15:640-643. 9. Kartus J, Movin T, Karlsson J. Donor-site morbidity and anterior knee problems after anterior cruciate ligament reconstruction using autografts. Arthroscopy 2001;17: 971-980. 10. Landes S, Nyland J, Elmlinger B, Tillett E, Caborn D. Knee flexor strength after ACL reconstruction: Comparison between hamstring autograft, tibialis anterior allograft, and non-injured controls. Knee Surg Sports Traumatol Arthrosc 2010;18:317-324. 11. Ejerhed L, Kartus J, Sernert N, Köhler K, Karlsson J. Patellar tendon or semitendinosus tendon autografts for anterior cruciate ligament reconstruction? A prospective randomized study with a two-year follow-up. Am J Sports Med 2003;31:19-25. 12. Järvelä T, Kannus P, Latvala K, Järvinen M. Simple measurements in assessing muscle performance after an ACL reconstruction. Int J Sports Med 2002;23:196-201. 13. Yasuda K, Ohkoshi Y, Tanabe Y, Kaneda K. Quantitative evaluation of knee instability and muscle strength after anterior cruciate ligament reconstruction using patellar and quadriceps tendon. Am J Sports Med 1992;20:471-475. 14. Seto JL, Orofino AS, Morrissey MC, Medeiros JM, Mason WJ. Assessment of quadriceps/hamstring strength, knee ligament stability, functional and sports activity levels five years after anterior cruciate ligament reconstruction. Am J Sports Med 1988;16:170-178. 15. Shino K, Nakata K, Horibe S, Inoue M, Nakagawa S. Quantitative evaluation after arthroscopic anterior cruciate ligament reconstruction. Allograft versus autograft. Am J Sports Med 1993;21:609-616.
16. Moisala AS, Järvelä T, Kannus P, Järvinen M. Muscle strength evaluations after ACL reconstruction. Int J Sports Med 2007;28:868-872. 17. Ko MS, Yang SJ, Ha JK, Choi JY, Kim JG. Correlation between hamstring flexor power restoration and functional performance test: 2-Year follow-up after ACL reconstruction using hamstring autograft. Knee Surg Relat Res 2012;24:113-119. 18. Luna NM, Alonso AC, Brech GC, Mochizuki L, Nakano EY, Greve JM. Isokinetic analysis of ankle and ground reaction forces in runners and triathletes. Clinics (Sao Paulo) 2012;67:1023-1028. 19. Baltzopoulos V, Brodie DA. Isokinetic dynamometry. Applications and limitations. Sports Med 1989;8:101-116. 20. Tashiro T, Kurosawa H, Kawakami A, Hikita A, Fukui N. Influence of medial hamstring tendon harvest on knee flexor strength after anterior cruciate ligament reconstruction. A detailed evaluation with comparison of single- and double-tendon harvest. Am J Sports Med 2003;31:522-529. 21. Eriksson K, Hamberg P, Jansson E, Larsson H, Shalabi A, Wredmark T. Semitendinosus muscle in anterior cruciate ligament surgery: Morphology and function. Arthroscopy 2001;17:808-817. 22. Rosenberg TD, Franklin JL, Baldwin GN, Nelson KA. Extensor mechanism function after patellar tendon graft harvest for anterior cruciate ligament reconstruction. Am J Sports Med 1992;20:519-525. 23. Åhlén M, Lidén M, Bovaller Å, Sernert N, Kartus J. Bilateral magnetic resonance imaging and functional assessment of the semitendinosus and gracilis tendons a minimum of 6 years after ipsilateral harvest for anterior cruciate ligament reconstruction. Am J Sports Med 2012;40: 1735-1741. 24. Lautamies R, Harilainen A, Kettunen J, Sandelin J, Kujala UM. Isokinetic quadriceps and hamstring muscle strength and knee function 5 years after anterior cruciate ligament reconstruction: Comparison between bonepatellar tendon-bone and hamstring tendon autografts. Knee Surg Sports Traumatol Arthrosc 2008;16:1009-1016. 25. Muneta T, Sekiya I, Ogiuchi T, Yagishita K, Yamamoto H, Shinomiya K. Objective factors affecting overall subjective evaluation of recovery after anterior cruciate ligament reconstruction. Scand J Med Sci Sports 1998;8:283-289. 26. Keays SL, Bullock-Saxton J, Keays AC, Newcombe P. Muscle strength and function before and after anterior cruciate ligament reconstruction using semitendinosus and gracilis. Knee 2001;8:229-234. 27. Reider B, Arcand MA, Diehl LH, et al. Proprioception of the knee before and after anterior cruciate ligament reconstruction. Arthroscopy 2003;19:2-12.
Purpose: The purpose of this study was to evaluate serial changes in quadriceps and hamstring muscle strength over the first postoperative year in patients who underwent anterior cruciate ligament (ACL) reconstruction with an autologous hamstring tendon graft and to reveal which of these 2 muscles lost more strength and recovered more slowly after autologous hamstring ACL reconstruction. Methods: Isokinetic muscle strength was measured preoperatively and at 6 months and 1 year postoperatively in 20 patients who underwent ACL reconstruction. The maximal torque (60 /s) and total work (180 /s) of the quadriceps and hamstring were evaluated using an isokinetic testing device. The isokinetic muscle strength and endurance of the injured legs were expressed as percentages of those of the uninjured legs at the same time point. Results: Both quadriceps and hamstring muscle strength at 60 /s and endurance at 180 /s of the injured relative to the uninjured leg was 50% preoperatively. Quadriceps muscle strength and endurance of the injured leg increased to 70% at 6 months and 80% at 1 year postoperatively, whereas hamstring muscle strength and endurance increased to 80% at 6 months and 80% at 1 year. Conclusions: Knee muscle strength recovered progressively after ACL reconstruction using autologous hamstring tendons but did not fully recover, being about 80% that of the uninjured leg even 1 year after surgery. Level of Evidence: Level IV, therapeutic case series.
T
he clinical outcomes of anterior cruciate ligament (ACL) reconstruction include recovery of muscle strength1,2 as well as the knee regaining good stability and sufficient range of motion.3,4 Despite the advantages of satisfactory tensile graft strength and tunnel fixation resulting from fast and strong bone-to-bone tunnel healing,5-7 the use of autologous boneepatellar tendonebone grafts has rapidly diminished because of
From the Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine (D-H.L), Seoul; and Sports Medical Center (J-H.L., H-J.J., S-J.L.), Korea University College of Medicine, Anam Hospital, Seoul, Republic of Korea. The authors report the following potential conflict of interest or source of funding: This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF2013R1A1A2A10010605), funded by the Ministry of Education, Science and Technology. This work was also supported by Korea University grant K1423281. Received May 1, 2014; accepted December 3, 2014. Address correspondence to Dae-Hee Lee, M.D., Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 135-710, Republic of Korea. E-mail: [email protected] Ó 2015 by the Arthroscopy Association of North America 0749-8063/14380/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.12.005
donor site morbidity, including anterior knee pain and patellar fracture,8-11 and long-term quadriceps femoris dysfunction even after 9 years.12 this has increased the use of quadruple hamstring tendons as a graft source. Use of a boneepatellar tendonebone autograft results in a postoperative decrease in knee extension strength13-15 followed by recovery over time, although losses of hamstring strength are minimal using this technique.16 In contrast, during hamstring autograft ACL reconstruction, loss of muscle strength after surgery is likely to be greater in the knee flexor than in the extensor because of harvesting of the hamstring tendon, although it has not yet been determined whether extensor (quadriceps) muscle strength decreases more than flexor (hamstring) muscle strength.17 In addition, the patterns of postoperative recovery of muscle strength from preoperative levels are also not clearly understood in patients who undergo autologous hamstring graft ACL reconstruction, because of a lack of data on preoperative muscle strength in previous studies. The purpose of this study was to evaluate serial changes over the first postoperative year in quadriceps and hamstring muscle strength in patients who underwent ACL reconstruction with an autologous
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hamstring tendon graft and to reveal which of these 2 muscles lost more strength and recovered more slowly after autologous hamstring ACL reconstruction. It was hypothesized that in patients who undergo autologous hamstring tendon graft ACL reconstruction, isokinetic knee muscle strength would recover progressively after surgery but would not recover fully, even after 1 year, and that the recovery of the knee flexor (hamstring) would be more delayed than that of the knee extensor (quadriceps) because hamstring harvesting would result in a greater deficit of hamstring than of quadriceps muscle strength.
Methods Study Design and Patient Enrollment This prospective longitudinal trial enrolled patients who were candidates for ACL reconstruction with 4-stranded hamstring autografts (gracilis plus semitendinosus) between 2011 and 2012. Patients were included only if they had unilateral isolated ACL rupture as confirmed by magnetic resonance imaging and physical examinations such as positive anterior draw, Lachman, and pivot shift tests (more than grade II), or a combination of examinations. Patients with ACL tears associated with meniscus tears were excluded to eliminate the bias resulting from meniscus tears. Also, patients with bilateral ACL injuries or concomitant injuries to any other ligament (i.e., the medial or lateral collateral ligament or the posterior cruciate ligament) or any associated extra-articular lesions were excluded. Patients were also excluded if they were unable to perform the isokinetic muscle strength test because of pain (usually caused by limited motion of the knee joint) resulting from an inadequate interval from injury (< 4 weeks). No nerve block was used at the time of surgery. Of the 27 patients (27 knees) approached, 25 agreed to take part in the study. After assessing for eligibility, 23 patients were enrolled. The final analysis involved data from 20 patients because 3 patients did not undergo complete isokinetic strength tests at the 3 time points (preoperatively and at 6 months and 1 year postoperatively). The baseline demographic characteristics of the participants are described in Table 1. The study protocol was approved by our institutional review board, and all participants provided written informed consent before participation.
Assessment of Isokinetic Strength All patients performed isokinetic muscle strength tests preoperatively and 6 months and 1 year postoperatively using a Biodex Multi-Joint System 4 (Biodex Medical Systems, Shirley, NY). The participants sat in an upright position on the dynamometer chair with a strap across the chest; they grasped the edge of the bench and flexed their hips and knees 90 each (Fig 1). The range of motion of the tested knee joint was set from full extension (0 ) to 100 flexion. Testing consisted of maximal concentric quadriceps/concentric hamstring reciprocal contractionsd5 at an angular velocity of 60 /s and 15 at 180 /sdwith a rest time of 30 seconds between tests. Before each test session, patients performed 5 warmup knee flexions and extensions for each leg at 60 /s. Peak torque, defined as the single highest point in the torque curve (N$m) of flexion and extension at 60 /s, was evaluated to determine muscle strength. Total work, defined as the sum total of the area under all torque
Table 1. Demographic Characteristics of Study Participants Number of male to female patients Age, yr (range) Height, cm (range) Weight, kg (range) Body mass index, kg/m2 (range) Time interval from injury to testing, mo (range)
15:5 30.5 (17-51) 170.1 (152-183) 73.3 (48-130) 25.8 (19.2-40.1) 5.1 5.3 (2-26)
Fig 1. Measurement of isokinetic muscle strength using a dynamometer.
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curves in the test repetitions (J) of flexion and extension at 180 /s, was evaluated to determine muscular endurance, defined as the ability of the muscles to perform repeated contractions against a load.18,19 Extensor strength and endurance were regarded as quadriceps strength and endurance, respectively, and flexor strength and endurance were regarded as hamstring strength and endurance, respectively. Especially when evaluating hamstring strength, an additional measurement of flexion torque at 90 was obtained from the torque curves recorded at 60 /s. This enabled an accurate evaluation of the recovery of hamstring strength at deep knee flexion, because insufficient hamstring muscle strength in deep knee flexion after ACL reconstruction with a hamstring tendon autograft has been reported.20,21 Two trials of each were performed, with their mean set as maximal peak torque and total work of the hamstring and quadriceps muscles. To analyze the recovery of muscle strength and endurance in the operated leg, the isokinetic muscle strength and endurance of this leg were expressed as percentages of those of the unoperated leg of the same patient at the same time point. Statistical Analysis A priori power analysis was performed to determine the sample size using the 2-sided hypothesis test at an alpha level of 0.05 and a power of 0.8. A pilot study of 5 knees found that the standard deviations for preoperative and 6-month postoperative isokinetic maximal torques of the quadriceps were 10% and 12%, respectively. We calculated that 17 knees were required to detect a 20% difference in the isokinetic maximal torque of the quadriceps from before surgery to 6 months after surgery, assuming the standard deviations taken from a pilot study of 5 knees. The current study finally involved 20 patients, indicating adequate power (0.885) for detecting a significant difference between the 2 evaluations.
Repeated-measures analysis of variance was used to evaluate changes in isokinetic muscle strength over time. This method takes into account outcome measurements over time and correlates successive outcomes. Post hoc Tukey tests were used to determine which 2 of the 3 time points differed significantly. All statistical analyses were performed using IBM SPSS Statistics, version 20 (SPSS, Chicago, IL). P < .05 was considered statistically significant.
Results
The peak torque at 60 /s and the total work at 180 /s of the quadriceps and hamstring muscles of both the involved and uninvolved limbs were higher 6 months and 1 year after than before ACL reconstruction. However, the hamstring to quadriceps ratios of both the involved and uninvolved limbs were similar before and after surgery (Table 2). The isokinetic maximal peak torques at 60 /s and endurance at 180 /s of the quadriceps and hamstring were significantly lower on the involved than on the uninvolved sides at all 3 time points. The quadriceps and hamstring maximal peak torques of the uninvolved leg versus the involved leg at 60 /s were, respectively, 185 versus 93 N$m (P < .001) and 90 versus 44 N$m (P < .001) preoperatively, 216 versus 153 N$m (P ¼ .003) and 112 versus 88 N$m (P < .001) at 6 months postoperatively, and 228 versus 178 N$m (P < .001) and 119 versus 93 N$m (P < .001) at 1 year postoperatively (Fig 2 A and B). The quadriceps and hamstring endurance of the uninvolved leg versus the involved leg at 180 /s were, respectively, 1,479 versus 742 J (P < .001) and 850 versus 363 J (P < .001) preoperatively, 1,608 versus 1,124 J (P < .001) and 945 versus 775 J (P ¼ .009) at 6 months postoperatively, and 1,681 versus 1,393 J (P < .001) and 1,042 versus 871 J (P < .001) at 1 year postoperatively (Fig 2 C and D). The quadriceps muscle strength at 60 /s and endurance at 180 /s of the injured leg compared with the uninjured leg increased significantly, being 50%
Table 2. Serial Changes in Muscle Strength and Hamstring to Quadriceps Ratios of Participants Who Underwent Anterior Cruciate Ligament Reconstruction Variable Quadriceps 60 , uninvolved leg, N$m Quadriceps 60 , involved leg, N$m Hamstring 60 , uninvolved leg, N$m Hamstring 60 , involved leg, N$m Hamstring to quadriceps ratio 60 , uninvolved leg Hamstring to quadriceps ratio 60 , involved leg Quadriceps 180 , uninvolved leg, J Quadriceps 180 , involved leg, J Hamstring 180 , uninvolved leg, J Hamstring 180 , involved leg, J Hamstring to quadriceps ratio 180 , uninvolved leg Hamstring to quadriceps ratio 180 , involved leg
Preoperative Status 185 47 93 51 90 31 44 31 52% 15% 64% 33% 1,479 456 742 432 850 346 363 309 58% 10% 60% 17%
NOTE. Data are expressed as mean SD unless otherwise indicated.
6 Mo Postoperatively 216 72 153 65 112 33 88 24 48% 9% 65% 18% 1,608 521 1,124 481 945 390 775 298 59% 12% 72% 16%
1 Yr Postoperatively 228 72 178 69 119 42 96 41 51% 7% 59% 13% 1,681 533 1,393 504 1,042 346 871 304 57% 15% 63% 13%
P Value .022 < .001 .009 < .001 .25 .23 .08 < .001 .028 < .001 .96 .09
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Fig 2. Isokinetic muscle strength and endurance on the involved and uninvolved sides in patients who underwent autologous hamstring anterior cruciate ligament (ACL) reconstruction preoperatively and 6 months and 1 year postoperatively. Maximal peak torques of the (A) quadriceps and (B) hamstring muscles at 60 /s. Total work of the (C) quadriceps and (D) hamstring muscles at 180 /s. (EX, extension; FL, flexion.)
preoperatively, 70% after 6 months, and 80% after 1 year. The hamstring muscle strength at 60 /s and endurance at 180 /s of the injured leg compared with the uninjured leg also increased significantly but with a slightly different pattern, being 50% preoperatively, 80% at 6 months, and 80% at 1 year. This recovery pattern of hamstring muscle strength was also seen at deep knee flexion of 100 (Table 3). The mean percentage quadriceps muscle strength and endurance of the injured leg compared with the uninjured leg increased significantly not only from before to 6 months after surgery but also between 6 months and 1 year postoperatively (Fig 3 A and B). In contrast, the mean percentage hamstring muscle strength and endurance of the injured leg compared with the uninjured leg increased significantly only from before surgery to 6 months after surgery but not from 6 months to 1 year (Fig 3 C and D). Compared with preoperative measurements of the uninjured knee, the mean quadriceps muscle strength of the injured knee at 60 /s was 81% 6 months after surgery and 94% after 1 year, whereas the quadriceps muscle endurance of the injured knee at 180 /s was 77% after
6 months and 95% after 1 year. In contrast, the mean hamstring muscle strength at 60 /s on the injured side was 170% after 6 months and 190% after 1 year compared with the preoperative hamstring muscle strength on the uninjured side, whereas the hamstring endurance at 180 /s on the injured side recovered to 97% after 6 months and to 113% after 1 year.
Discussion The most important finding of the present study was that isokinetic knee muscle strength recovered progressively after hamstring-harvested ACL reconstruction but did not recover fully even 1 year after surgery. In addition, the results showed that hamstring strength recovered faster than quadriceps strength, despite harvesting of the autologous hamstring. Losses in quadriceps strength have been reported to be approximately 10% greater than losses in hamstring strength after ACL reconstruction using autologous patellar tendon grafts.22 In patients undergoing ACL reconstruction with autologous hamstring grafts, we hypothesized that because of hamstring harvesting, knee flexion (hamstring) strength would be more
Table 3. Serial Changes in Muscle Strength and Endurance Expressed as the Percentage of Injured to Uninjured Limb Before and After Surgery Variable Quadriceps 60 percentage, involved/uninvolved legs 100, % Hamstring 60 percentage, involved/uninvolved legs 100, % Quadriceps 180 percentage, involved/uninvolved legs 100, % Quadriceps 180 percentage, involved/uninvolved legs 100, % Hamstring percentage, 100 flexion, involved/uninvolved legs 100, % NOTE. Data are expressed as mean SD unless otherwise indicated.
Preoperative Status 49 22 49 37 51 26 51 40 51 37
6 Mo Postoperatively 66 21 79 14 71 22 80 19 77 30
1 Yr Postoperatively 78 23 80 24 84 17 85 13 82 27
P Value .002 .001 .001 .018 < .001
KNEE MUSCLE STRENGTH AFTER ACL RECONSTRUCTION
Fig 3. Serial changes in muscle strength and endurance percentages of the (A and B) quadriceps and (C and D) hamstring muscles of the injured leg compared with the uninjured leg.
decreased postoperatively than knee extension (quadriceps) strength. Contrary to our hypothesis, however, we observed a greater loss in quadriceps muscle strength than in hamstring muscle strength after 1 year in 20 patients who underwent quadruple hamstring tendon ACL reconstruction. These results were consistent with the Eriksson et al.21 study evaluating 16 autologous hamstring ACL reconstructions, which found that the deficit in quadriceps strength was greater than the deficit in hamstring strength after a minimum of 6 months.21 The reason for the better recovery of hamstring than quadriceps strength is unclear but may result from the greater reduction in quadriceps than hamstring muscle volume after ACL reconstruction, with the former decreasing about 10%. In addition, the neotendon that regenerates at the site of the hamstring tendon could reduce and compensate for losses in hamstring muscle strength caused by hamstring harvesting.21,23 Previous studies24,25 have shown greater losses in quadriceps than hamstring strength after ACL reconstruction with autologous patellar tendons, along with slower recovery of quadriceps strength than hamstring strength. A study of serial changes in muscle performance in patients who underwent autologous patellar tendon ACL reconstruction showed that postoperative quadriceps strength on the injured side was approximately 60% after 6 months, 70% after 1 year, and 90% after 2 years compared with the uninjured side.3 In contrast, the hamstring strength of the operated leg was about 90% to 95% that of the contralateral leg after 6 months, with this strength maintained thereafter. To our knowledge, only one previous study has assessed changes over time in isokinetic knee muscle strength from before to after ACL reconstruction with autologous hamstring tendons. A study of 31 participants found that the mean preoperative quadriceps and hamstring strength of the injured leg was 93% and nearly 100%, respectively, that of the uninjured leg
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because of a 6- to 8-week preoperative physiotherapy program.26 Postoperative quadriceps and hamstring strength of the injured leg 6 months after surgery decreased to about 90% that of the uninjured leg, suggesting that recovery of hamstring strength was slower than that of quadriceps strength because of hamstring harvest for ACL grafts. However, the followup period (6 months) of that study was too short to show progressive recovery patterns of muscle strength after ACL reconstruction. In contrast to previous results,26 we found that recovery of isokinetic quadriceps performance was slower than that of hamstring performance, even when the graft was harvested from the hamstring. However, caution should be exercised in comparing the results of these studies because of differences in the time interval from injury to surgery and pre- and postoperative rehabilitation protocols. Limitations This study had several limitations. One of the most important limitations was the lack of a healthy control group. However, it is very difficult to select control participants with the same activity level or athletic history as participants with ACL tears. Rather, data from the uninvolved side were used as a control for the involved side. However, bilateral muscle strength impairment was possible, suggesting that aberrant afferent information in the intra-articular receptors in the injured limb may also affect muscle strength in the contralateral uninjured limb.27 Another limitation was that we did not assess the relationships between serial changes in muscle strength and clinical outcomes; however, that was not the primary aim of this study. Finally, the isokinetic muscle strength and endurance measured in this study may be insufficient to reflect patients’ activities of daily life, including physical labor and participation in sports.
Conclusions Knee muscle strength recovered progressively after ACL reconstruction using autologous hamstring tendons but did not fully recover, being about 80% that of the uninjured leg even 1 year after surgery.
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