341
The
patella
The patella is the larger of two named sesamoid bones in man (the other is the fabella). In the 1930s it was regarded as a redundant structure,’ but subsequent work has shown how important it is to the normal function of the knee joint. The patella is prone to a variety of ills; the two commonest being anterior knee pain and osteoarthritis of the patellofemoral joint.2 Management of both conditions is influenced by the blood supply and biomechanics of this curious bone. There is evidence that pain in the patella, as in the hlp3’° and back,5 is associated with raised intraosseous pressure.’ Pressure is raised both in anterior knee pain and in osteoarthritis,but the underlying mechanism is not understood. Although arteriolar arcades in the subchondral bone of the patella are disrupted in osteoarthritis/,8 whether this process is related to alterations in intraosseous pressure is unclear since such disruption does not occur in chondromalacia patellae.8 The dynamics of bone blood flow are difficult to investigate; few data are available, and none for the patella. Raised intraosseous pressure is reduced by osteotomy of the patella, a technique that is used to relieve pain in both anterior knee pain and 6
osteoarthritis. Osteotomy is generally regarded as a way to alter the biomechanics of the patello-femoral joint rather than a means of reducing intraosseous pressure. Contact stress has been measured with pressure-sensitive film in vitro,9lo but it is unlikely that this approach can mimic the dynamics of the enormous loads placed on the joint in vivo. Most biochemical investigations have been carried out on cadaver knees and have concentrated on the measurement of movement in the sagittal plane. In one study," investigators inserted intracortical pins into the three principal bones of the knee joint of volunteers, and were able to show movements in other planes, including an important medial translation of the patella in the intercondylar notch when the heel strikes the ground. This observation may explain why, in chondromalacia patellae, articular changes are found on the medial and odd facets of the patella, but does not shed any light on the biomechanical consequences of patellar osteotomy. In older patients osteoarthritis of the patellofemoral joint is often accompanied by osteoarthritis of the tibiofemoral joint, and total knee replacement may be advised. With such surgery it is also important to minimise the stresses placed on the patella. Most patellar prostheses are little more than plastic and metal buttons added to the design as an afterthought, and take little account of the biomechanics of the patella. Some investigators judge that an attempt to mimic the articular surface of the patella confers no advantage, but this may reflect inadequacies in the design. Patellofemoral complications are probably one of the commonest causes of failed total knee replacement. Slater and colleagues8 have argued that interference in the normal vascular arcades may
adversely affect the healing of patellar prostheses used in total knee replacement. Overall, loosening is probably due to the biomechanical properties of the patellofemoral joint and not to altered blood flow patterns. It should come as no surprise that forces in this heavily stressed joint (the knee has the thickest articular cartilage of any human joint2) should precipitate loosening, and that the reliability of patellar replacements is controversial.12,13 Sadly, most of our interventions on the patella are empirical, and are supported more by the enthusiasm of proponents than by a very deep knowledge of the biology or biomechanics of this unusual joint. The knee cap could do with more scientific attention.
1. Brooke R. The treatment of fractured patella by excision. A study of morphology and function. Br J Surg 1937; 24: 753-47. 2. Meacham G, Emery IH. Quantitative aspects of patello-femoral cartilage fibrillation in Liverpool necropsies. Ann Rheum Dis 1974; 33: 39-47. 3. Termansen NB, Teglbjaerg PS, Sorensen KH. Primary osteoarthritis of the hip: interrelationship between intraosseous pressure, X-ray
changes, clinical severity, and bone density. Acta Orthop Scand 1981; 52: 215-22. 4. Pedersen NW, Kiaer
T, Kristensen KD, Starklint H. Intraosseous oxygenation and histology in arthrosis and osteonecrosis of the hip. Acta Orthop Scand 1989; 60: 415-17. pressure,
patients with lumbar pain. Acta Orthop Scand 1972; 43: 109-17. 6. Hejgaard N, Amoldi CC. Osteotomy of the patella in the patellofemoral pain syndrome. The significance of increased intraosseous pressure during sustained knee flexion. Int Orthop 1984; 8: 189-94. 7. Björkstrom S, Goldie IF. A study of the arterial supply of the patella in the normal state, in chondromalacia patellae and in osteoarthritis. Acta Orthop Scand 1980; 51: 63-70. 8. Slater RNS, Spencer JD, Churchill MA, Bridgemann GP, Brookes M. Observations on the intrinsic blood supply to the human patella: disruption correlated with articular surface degeneration. J R Soc Med 5. Arnoldi CC. Intravertebral pressure in
1991; 84: 606-07. 9. Ahmed AM. A pressure distribution transducer for in-vitro static measurements of synovial joints. J Eden Eng 1983; 105: 309-14. 10. Huberti HH, Hayes WC. Patellofemoral contact pressures: the influence of Q angle and tendo femoral contact. J Bone Jt Surg 1984; 66A: 715-24. 11. LaFortune MA, Cavanagh PR. The measurement of normal knee joint motion during walking using intracortical pins. In: Whittle N, Harris D, eds. Biomechanical measurement in orthopaedic practice. Oxford: Clarendon, 1985: 234-43. 12. Ranawat CS. The patellofemoral joint in total condylar knee arthroplasty. Clin Orthop Rel Res 1986; 205: 93-99. 13. Goldberg VM, Figgie HE, Veregge P, Singerman R, Davy D. Surgical considerations in patellar replacement. In: Goldberg VM, ed. Controversies in total knee arthroplasty. New York: Raven, 1990.
More music in The Lancet: Stroke Octet Last year Prof Charles Warlow contacted us about the possibility of another musical excursion along the lines of our 1990 Epilepsy Octet. "Could yousomeday-be persuaded to do the same sort of thing for stroke?" he inquired. We needed little persuasion. Professor Warlow (he needed little persuasion) duly agreed to coordinate the venture for us and promptly assembled an international team of contributors. We thank the authors, who kept to length and to deadlines, and hope readers are pleased with the outcome (fourteen articles spread over eight issues). We begin, on the next page, with a duo.
The
patella
The patella is the larger of two named sesamoid bones in man (the other is the fabella). In the 1930s it was regarded as a redundant structure,’ but subsequent work has shown how important it is to the normal function of the knee joint. The patella is prone to a variety of ills; the two commonest being anterior knee pain and osteoarthritis of the patellofemoral joint.2 Management of both conditions is influenced by the blood supply and biomechanics of this curious bone. There is evidence that pain in the patella, as in the hlp3’° and back,5 is associated with raised intraosseous pressure.’ Pressure is raised both in anterior knee pain and in osteoarthritis,but the underlying mechanism is not understood. Although arteriolar arcades in the subchondral bone of the patella are disrupted in osteoarthritis/,8 whether this process is related to alterations in intraosseous pressure is unclear since such disruption does not occur in chondromalacia patellae.8 The dynamics of bone blood flow are difficult to investigate; few data are available, and none for the patella. Raised intraosseous pressure is reduced by osteotomy of the patella, a technique that is used to relieve pain in both anterior knee pain and 6
osteoarthritis. Osteotomy is generally regarded as a way to alter the biomechanics of the patello-femoral joint rather than a means of reducing intraosseous pressure. Contact stress has been measured with pressure-sensitive film in vitro,9lo but it is unlikely that this approach can mimic the dynamics of the enormous loads placed on the joint in vivo. Most biochemical investigations have been carried out on cadaver knees and have concentrated on the measurement of movement in the sagittal plane. In one study," investigators inserted intracortical pins into the three principal bones of the knee joint of volunteers, and were able to show movements in other planes, including an important medial translation of the patella in the intercondylar notch when the heel strikes the ground. This observation may explain why, in chondromalacia patellae, articular changes are found on the medial and odd facets of the patella, but does not shed any light on the biomechanical consequences of patellar osteotomy. In older patients osteoarthritis of the patellofemoral joint is often accompanied by osteoarthritis of the tibiofemoral joint, and total knee replacement may be advised. With such surgery it is also important to minimise the stresses placed on the patella. Most patellar prostheses are little more than plastic and metal buttons added to the design as an afterthought, and take little account of the biomechanics of the patella. Some investigators judge that an attempt to mimic the articular surface of the patella confers no advantage, but this may reflect inadequacies in the design. Patellofemoral complications are probably one of the commonest causes of failed total knee replacement. Slater and colleagues8 have argued that interference in the normal vascular arcades may
adversely affect the healing of patellar prostheses used in total knee replacement. Overall, loosening is probably due to the biomechanical properties of the patellofemoral joint and not to altered blood flow patterns. It should come as no surprise that forces in this heavily stressed joint (the knee has the thickest articular cartilage of any human joint2) should precipitate loosening, and that the reliability of patellar replacements is controversial.12,13 Sadly, most of our interventions on the patella are empirical, and are supported more by the enthusiasm of proponents than by a very deep knowledge of the biology or biomechanics of this unusual joint. The knee cap could do with more scientific attention.
1. Brooke R. The treatment of fractured patella by excision. A study of morphology and function. Br J Surg 1937; 24: 753-47. 2. Meacham G, Emery IH. Quantitative aspects of patello-femoral cartilage fibrillation in Liverpool necropsies. Ann Rheum Dis 1974; 33: 39-47. 3. Termansen NB, Teglbjaerg PS, Sorensen KH. Primary osteoarthritis of the hip: interrelationship between intraosseous pressure, X-ray
changes, clinical severity, and bone density. Acta Orthop Scand 1981; 52: 215-22. 4. Pedersen NW, Kiaer
T, Kristensen KD, Starklint H. Intraosseous oxygenation and histology in arthrosis and osteonecrosis of the hip. Acta Orthop Scand 1989; 60: 415-17. pressure,
patients with lumbar pain. Acta Orthop Scand 1972; 43: 109-17. 6. Hejgaard N, Amoldi CC. Osteotomy of the patella in the patellofemoral pain syndrome. The significance of increased intraosseous pressure during sustained knee flexion. Int Orthop 1984; 8: 189-94. 7. Björkstrom S, Goldie IF. A study of the arterial supply of the patella in the normal state, in chondromalacia patellae and in osteoarthritis. Acta Orthop Scand 1980; 51: 63-70. 8. Slater RNS, Spencer JD, Churchill MA, Bridgemann GP, Brookes M. Observations on the intrinsic blood supply to the human patella: disruption correlated with articular surface degeneration. J R Soc Med 5. Arnoldi CC. Intravertebral pressure in
1991; 84: 606-07. 9. Ahmed AM. A pressure distribution transducer for in-vitro static measurements of synovial joints. J Eden Eng 1983; 105: 309-14. 10. Huberti HH, Hayes WC. Patellofemoral contact pressures: the influence of Q angle and tendo femoral contact. J Bone Jt Surg 1984; 66A: 715-24. 11. LaFortune MA, Cavanagh PR. The measurement of normal knee joint motion during walking using intracortical pins. In: Whittle N, Harris D, eds. Biomechanical measurement in orthopaedic practice. Oxford: Clarendon, 1985: 234-43. 12. Ranawat CS. The patellofemoral joint in total condylar knee arthroplasty. Clin Orthop Rel Res 1986; 205: 93-99. 13. Goldberg VM, Figgie HE, Veregge P, Singerman R, Davy D. Surgical considerations in patellar replacement. In: Goldberg VM, ed. Controversies in total knee arthroplasty. New York: Raven, 1990.
More music in The Lancet: Stroke Octet Last year Prof Charles Warlow contacted us about the possibility of another musical excursion along the lines of our 1990 Epilepsy Octet. "Could yousomeday-be persuaded to do the same sort of thing for stroke?" he inquired. We needed little persuasion. Professor Warlow (he needed little persuasion) duly agreed to coordinate the venture for us and promptly assembled an international team of contributors. We thank the authors, who kept to length and to deadlines, and hope readers are pleased with the outcome (fourteen articles spread over eight issues). We begin, on the next page, with a duo.
