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Patellar tendon avulsion after total knee arthroplasty
The JournalofArthroplastyVol. 10 No. 3 1995
Patellar T e n d o n A v u l s i o n A f t e r Total K n e e A r t h r o p l a s t y A New Technique J. C. A b r i l , M D , L. A l v a r e z , M D , a n d J. C. V a l l e j o , M D
Abstract: Patellar tendon avulsion is a rare complication of total knee arthroplasty. An
easy surgical technique that involves suturing the tendon into a groove carved in the tibial tubercle and tension band wiring is described. Two cases are presented, with an average follow-up period of 21 months. Good clinical results were obtained in each case. No postoperative complications occurred. Key words: total knee arthroplasty, patellar tendon avulsion.
Avulsion of the patellar t e n d o n after total knee arthroplasty (TKA) is an infrequent but serious complication. It has b e e n reported in 58 cases of knee arthroplasties (Table 1), T M but the causes, m a n a g e m e n t , and functional results have received little attention in the literature. Avulsion of the patellar t e n d o n after TIgoA remains problematic, as the best t r e a t m e n t of this complication is still uncertain. Because of the unsuccessful results reported for the use of other techniques, including augmentation with either autogenous or allograft t e n d o n tissue, suture, staples, semitendinosus reconstruction, and complete allograft replacement, we developed a n e w technique using direct repair of the t e n d o n to bone and neutralization of the repair with a tension band wire.
Operative Technique The incision from the previous surgery is followed to expose the avulsed ligament. Adhesions
From the Department of Orthopedic Surgery and Traumatology, Fundaci6n Jimdnez D[az, Universidad Aut6noma, Madrid, Spain. Reprint requests: J. C. Abril, MD, Departamento C.O.T., Fundaci6n Jimdnez Dfaz, Avda. Reyes Cat61icos, n °~. 2, 28040 Madrid, Spain.
are lysed to mobilize the patella. The position of the patella is determined by measuring both the length of the patella from the superior to the inferior pole and the distance from the inferior pole to the tibial tubercle (intraoperative radiographic Insall-Salvati ratio) .15 With a chisel, a groove is carved in the superior aspect of the tibial tubercle (from the proximal end to the distal end) about 1.5 cm long. The patellar t e n d o n is s u t u r e d w i t h n o n a b s o r b a b l e suture (Ethibon) according to Bunnell's technique 16 (Fig. 1). The t e n d o n is placed in the groove and the two final end sutures are passed t h r o u g h to previously drilled bone holes. A tension (figure-of-eight) band wiring of the knee extensor m e c h a n i s m is implem e n t e d with the knee positioned in flexion to 45 ° (Fig. 2). The suture is t h e n tied to the bone surface. After surgery, the knee is not immobilized and isometric quadriceps rehabilitation is begun the day after the operation with straight-leg raising. Full weight bearing with crutches is b e g u n within 48 hours of the operation. The tension band wiring limits the flexion to 45 °, and a patella infera can be seen on postoperative radiographs. Three m o n t h s after the operation, the tension band wiring is removed, and walking w i t h o u t crutches is allowed. Progressive range of m o t i o n exercises are encouraged.
276
The Journal ofArthroplasty Vol, 10 No. 3 June 1995 T a b l e 1. R e p o r t s o f P a t e l l a r T e n d o n A v u l s i o n s A f t e r T K A Study
Year
Wilson t Lettin 2 Gibbs 3 Yamamoto 4 Wilson ~ Kaufer 6 Lettin 7 Oglesbys Oglesby~ Townley 9 Webster ~° Gustillo and T h o m p s o n n Rand et al. 12 E m e r s o n et al. ~3 Cadambi and Engh 14 This study
1976 1978 1979 1979 I980 1981 1984 1984 1984 1985 1985 1987 1989 1990 1992 1993
N u m b e r of R u p t u r e s 3 4 1 1 4 1 1 4 1 2 1 2 18 8 7 2
N u m b e r of TKAs 142 100 75 170 62 82 20 90 39 532 376 -8,288 -915 227
Percentage 2.1 4 1.3 0.5 6.4 1.2 5 4.4 2.5 0.4 0.2 0.2 0.5* 0.8
*Three patients were referred by outside physicians.
..i F i g . 1. S u r g i c a l t e c h n i q u e . N o t e t h e (A) t e n d o n s u t u r e a n d b o n e h o l e s a n d (B) f i g u r e - o f - e i g h t w i r e s u p p o r t a r o u n d t h e patella.
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Case Reports
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277
months, she has full extension with 95 ° of flexion and is fully ambulatory w i t h o u t aids.
Case 1 A 60-year-old w o m a n with osteoarthritis in her right knee had u n d e r g o n e a valgus osteotomy. Seven-years later, because of progressive arthritis, an u n c e m e n t e d total knee prosthesis was implanted. One m o n t h later, during rehabilitation, she suffered sudden loss of knee extension. A disrupted extensor m e c h a n i s m was diagnosed (Fig. 2A). During surgery, an avulsion of the patellar t e n d o n was observed, and the lesion was repaired employing the t e c h n i q u e previously described (Fig. 2B). After a follow-up period of 2 years, she has full extension and flexion of 85 ° and is walking w i t h o u t supports (ie, she has r e t u r n e d to her previous level of function).
Case 2 A 66-year-old w o m a n with osteoarthritis in her left knee u n d e r w e n t knee arthroplasty using an u n c e m e n t e d total condylar knee prosthesis. Three years later, the tibial c o m p o n e n t collapsed. It was treated by revision of the tibial c o m p o n e n t with a n e w plate implanted over a wedge of allograft. During surgery, an avulsion of the patellar t e n d o n occurred and was repaired with a staple. During rehabilitation 4 weeks later, she had failure of the staple fixation (Fig. 3A) and was treated with the t e c h n i q u e described above (Fig. 3B). After 18
Results Both patients were initially ambulatory with cane support and did not require other aids 3 m o n t h s after surgery. They p e r f o r m e d the standard rehabilitation over a 6 - m o n t h period. Their Hospital for Special Surgery postoperative clinical scores were 68 and 70, respectively. Preoperative average knee flexion was 90 °, and postoperative average knee flexion was 87 ° (85 ° a n d 90 °, respectively.). In both patients, the surgical t e c h n i q u e used was as described above, including figure-of-eight wire support. All patients experienced complete loss of active extension before reconstruction. After surgery, they e x t e n d e d their respective knees actively to the same degree as with passive extension. No complications were noted. Although the Insall-Salvati ratio 15 was initially less t h a n 1, it r e t u r n e d to normal after the figure-of-eight wire support was removed.
Discussion Patellar t e n d o n rupture after TKA is an uncomm o n event. The most frequently implicated etiologies are (1) attempts to gain wide exposure in a knee with limited m o t i o n Y ,I2,14 (2) distal patellar t e n d o n realignment for patellar dislocation, ~2 (3) implant
Fig. 2. (A) Preoperative lateral radiograph of case 1. Note that the Insall-Salvati ratio is increased. (B) Postoperative lateral radiograph showing the normal position of the patella.
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The Journal ofArthroplasty Vol. 10 No. 3 June 1995
Fig. 3. (A) Preoperative radiograph ol case 2 showing the position of the patella. (B) Postoperative radiograph after repair of the patellar tendon avulsion.
design a n d c o m p o n e n t alignment, 9,17 a n d (4) i m p i n g e m e n t of the prosthesis on the tendon, n Dilferent techniques h a v e b e e n reported in the literature, b u t no one has obtained consistent clinical success. Primary sutures, z7,8,1°,12 staple repair, 4'12 semitendinosus a u g m e n t a t i o n , 11,xz14 plantaris augmentation, 1 distal extensor m e c h a n i s m allograft, 13 carbon-fiber graft, xs'~9 bovine x e n o g r a f t ] 2,2° and expectant t r e a t m e n t w i t h o u t repair a,6,x2 or with extension casting 8 h a v e all yielded m i x e d results. Of 18 knees in a series reported by Rand et al., ~ 16 u n d e r w e n t reconstruction by p r i m a r y suture; however, only 4 (25%) w e r e successful. Two failed repairs w e r e c o n v e r t e d arthrodeses, and one septic case required an a b o v e - k n e e a m p u t a t i o n . In their series of 13 knees, E m e r s o n et al. e m p l o y e d a n e w a n d aggressive technique involving allograft distal extensor m e c h a n i s m reconstruction.13 The composite graft consisted of a quadriceps tendon, a patella with a c e m e n t e d prosthesis, a patellar tendon, a n d a tibial tubercle. Rupture of the quadriceps junction occurred once a n d was resutured, a n d r u p t u r e of the graft occurred on one occasion. Knee extension p o w e r a n d i m p r o v e d function w e r e achieved in the r e m a i n i n g cases, although m i n i m a l extensor lag was present in three cases. Gustillo a n d T h o m p s o n reported on patellar tendon ruptures in two elderly patients w i t h TKA, one of w h o m experienced a r e r u p t u r e after repair, n Both w e r e treated w i t h p r i m a r y sutures that connected the semitendinosus graft to a figure-of-eight wire support. Cadambi a n d Engh treated seven patients using a n a u t o g e n o u s graft of the semitendinosus tendon. 14 Although the semitendinosus graft has only
40 to 50% of the strength of a patellar ligament graft, the patients regained control of quadriceps function a n d extensor strength. Other authors r e c o m m e n d i n g suture or staple repair of the t e n d o n reported consistently p o o r outcomes, ls-20 We h a v e described an easy surgical technique that allows a s h o r t - t e r m r e t u r n of functional extensor power. Both of our patients progressed rapidly with standard rehabilitation p r o g r a m s a n d h a v e retained extensor p o w e r w i t h o u t lag after a followup period of 2 years. Although repair is technically feasible a n d yields good clinical results, in cases w h e r e e x t e n d e d exposure of the k n e e is required, p r e v e n t i o n of a rupture by p l a c e m e n t of a Kirschner wire in the tendon is preferred.
References 1. Wilson FC: Results of knee replacement with Walldius prosthesis: an interim report. Clin Orthop 120:39, 1976 2. Lettin AWF: The Stanmore hinged knee arthroplasty. J Bone Joint Surg 60B:327, 1978 3. Gibbs AN: A comparison of the Freeman-Swanson (ICLI-I) and Walldius prostheses in total knee replacement. J Bone Joint Surg 61B:358, 1979 4. Yamamoto S: Total knee replacement with KodamaYamamoto knee prosthesis. Clin Orthop 145:60, 1979 5. Wilson FC: Results of knee replacement with the Walldius and geometric prostheses: a comparative study. J Bone Joint Surg 62A:497, 1980 6. Kaufer H: Spherocentric arthroplasty of the knee: clinical experience with an average four-year followup. J Bone Joint Surg 63A:545, 1981
PatellarTendonAvulsion
7. Lettin AWF: The long-term results of Stanmore total knee replacements. J Bone Joint Surg 66B:349, 1984 8. Oglesby JW: The evolution of knee arthroplasty with three generations of prostheses. Clin Orthop 186:96, 1984
9. Townley CO: The anatomic total knee resurfacing arthroplasty. Clin Orthop 192:82, 1985 10. Webster DA: Complications of variable axis in total knee arthroplasty. Clin Orthop 193:160, 1985 11. Gustillo R, Thompson R: Quadriceps and patellar tendon ruptures following total knee arthroplasty, p. 41. In Rand JA, Dorr LD (eds): Total arthroplasty of the knee: proceedings of the Knee Society, 1985-1986. Aspen, Rockville, MD, 1987 12. Rand JA, Morrey BF, Bryan RS: Patellar tendon rupture after total knee arthroplasty. Clin Orthop 244:233, 1989 13. Emerson RH Jr, Head WC, Malinin TI: Reconstruction of patellar tendon rupture after total knee arthroplasty with an extensor mechanism allograft. Clin Orthop 260:154, 1990
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Abril et al.
279
14. Cadambi BA, Engh GA: Use of a semitendinosus tendon autogenous graft for rupture of the patellar ligam e n t after total knee arthroplasty. J Bone Joint Surg 74A:974, 1992 15. Insall J, Salvati E: Patella position in the normal knee joint. Radiology 101:101, 1971 16. Bunnell S: The early treatment of h a n d injuries. J Bone Joint Surg 33A:807, 1951 17. Figgie HE: The effect of alignment of the implant in fractures of the patella after condylar total knee arthroplasty. J Bone Joint Surg 71A:1031, 1989 18. Jenkins DHR: The role of flexible carbon-fibre implants as tendon and ligament substitutes in clinical practice: preliminary report. J Bone Joint Surg 62B:497, 1980 19. Keating EM: Use of carbon fiber implant as a knee extensor mechanism replacement in parts: a biomechanical study. Orthop Trans 7:281, 1983 20. A b b i n k EP: P r e l i m i n a r y r e p o r t on the use of xenografts in the knee instability problems. Orthop Trans 7:84, 1983
Patellar T e n d o n A v u l s i o n A f t e r Total K n e e A r t h r o p l a s t y A New Technique J. C. A b r i l , M D , L. A l v a r e z , M D , a n d J. C. V a l l e j o , M D
Abstract: Patellar tendon avulsion is a rare complication of total knee arthroplasty. An
easy surgical technique that involves suturing the tendon into a groove carved in the tibial tubercle and tension band wiring is described. Two cases are presented, with an average follow-up period of 21 months. Good clinical results were obtained in each case. No postoperative complications occurred. Key words: total knee arthroplasty, patellar tendon avulsion.
Avulsion of the patellar t e n d o n after total knee arthroplasty (TKA) is an infrequent but serious complication. It has b e e n reported in 58 cases of knee arthroplasties (Table 1), T M but the causes, m a n a g e m e n t , and functional results have received little attention in the literature. Avulsion of the patellar t e n d o n after TIgoA remains problematic, as the best t r e a t m e n t of this complication is still uncertain. Because of the unsuccessful results reported for the use of other techniques, including augmentation with either autogenous or allograft t e n d o n tissue, suture, staples, semitendinosus reconstruction, and complete allograft replacement, we developed a n e w technique using direct repair of the t e n d o n to bone and neutralization of the repair with a tension band wire.
Operative Technique The incision from the previous surgery is followed to expose the avulsed ligament. Adhesions
From the Department of Orthopedic Surgery and Traumatology, Fundaci6n Jimdnez D[az, Universidad Aut6noma, Madrid, Spain. Reprint requests: J. C. Abril, MD, Departamento C.O.T., Fundaci6n Jimdnez Dfaz, Avda. Reyes Cat61icos, n °~. 2, 28040 Madrid, Spain.
are lysed to mobilize the patella. The position of the patella is determined by measuring both the length of the patella from the superior to the inferior pole and the distance from the inferior pole to the tibial tubercle (intraoperative radiographic Insall-Salvati ratio) .15 With a chisel, a groove is carved in the superior aspect of the tibial tubercle (from the proximal end to the distal end) about 1.5 cm long. The patellar t e n d o n is s u t u r e d w i t h n o n a b s o r b a b l e suture (Ethibon) according to Bunnell's technique 16 (Fig. 1). The t e n d o n is placed in the groove and the two final end sutures are passed t h r o u g h to previously drilled bone holes. A tension (figure-of-eight) band wiring of the knee extensor m e c h a n i s m is implem e n t e d with the knee positioned in flexion to 45 ° (Fig. 2). The suture is t h e n tied to the bone surface. After surgery, the knee is not immobilized and isometric quadriceps rehabilitation is begun the day after the operation with straight-leg raising. Full weight bearing with crutches is b e g u n within 48 hours of the operation. The tension band wiring limits the flexion to 45 °, and a patella infera can be seen on postoperative radiographs. Three m o n t h s after the operation, the tension band wiring is removed, and walking w i t h o u t crutches is allowed. Progressive range of m o t i o n exercises are encouraged.
276
The Journal ofArthroplasty Vol, 10 No. 3 June 1995 T a b l e 1. R e p o r t s o f P a t e l l a r T e n d o n A v u l s i o n s A f t e r T K A Study
Year
Wilson t Lettin 2 Gibbs 3 Yamamoto 4 Wilson ~ Kaufer 6 Lettin 7 Oglesbys Oglesby~ Townley 9 Webster ~° Gustillo and T h o m p s o n n Rand et al. 12 E m e r s o n et al. ~3 Cadambi and Engh 14 This study
1976 1978 1979 1979 I980 1981 1984 1984 1984 1985 1985 1987 1989 1990 1992 1993
N u m b e r of R u p t u r e s 3 4 1 1 4 1 1 4 1 2 1 2 18 8 7 2
N u m b e r of TKAs 142 100 75 170 62 82 20 90 39 532 376 -8,288 -915 227
Percentage 2.1 4 1.3 0.5 6.4 1.2 5 4.4 2.5 0.4 0.2 0.2 0.5* 0.8
*Three patients were referred by outside physicians.
..i F i g . 1. S u r g i c a l t e c h n i q u e . N o t e t h e (A) t e n d o n s u t u r e a n d b o n e h o l e s a n d (B) f i g u r e - o f - e i g h t w i r e s u p p o r t a r o u n d t h e patella.
Patellar Tendon Avulsion
Case Reports
•
Abril et al.
277
months, she has full extension with 95 ° of flexion and is fully ambulatory w i t h o u t aids.
Case 1 A 60-year-old w o m a n with osteoarthritis in her right knee had u n d e r g o n e a valgus osteotomy. Seven-years later, because of progressive arthritis, an u n c e m e n t e d total knee prosthesis was implanted. One m o n t h later, during rehabilitation, she suffered sudden loss of knee extension. A disrupted extensor m e c h a n i s m was diagnosed (Fig. 2A). During surgery, an avulsion of the patellar t e n d o n was observed, and the lesion was repaired employing the t e c h n i q u e previously described (Fig. 2B). After a follow-up period of 2 years, she has full extension and flexion of 85 ° and is walking w i t h o u t supports (ie, she has r e t u r n e d to her previous level of function).
Case 2 A 66-year-old w o m a n with osteoarthritis in her left knee u n d e r w e n t knee arthroplasty using an u n c e m e n t e d total condylar knee prosthesis. Three years later, the tibial c o m p o n e n t collapsed. It was treated by revision of the tibial c o m p o n e n t with a n e w plate implanted over a wedge of allograft. During surgery, an avulsion of the patellar t e n d o n occurred and was repaired with a staple. During rehabilitation 4 weeks later, she had failure of the staple fixation (Fig. 3A) and was treated with the t e c h n i q u e described above (Fig. 3B). After 18
Results Both patients were initially ambulatory with cane support and did not require other aids 3 m o n t h s after surgery. They p e r f o r m e d the standard rehabilitation over a 6 - m o n t h period. Their Hospital for Special Surgery postoperative clinical scores were 68 and 70, respectively. Preoperative average knee flexion was 90 °, and postoperative average knee flexion was 87 ° (85 ° a n d 90 °, respectively.). In both patients, the surgical t e c h n i q u e used was as described above, including figure-of-eight wire support. All patients experienced complete loss of active extension before reconstruction. After surgery, they e x t e n d e d their respective knees actively to the same degree as with passive extension. No complications were noted. Although the Insall-Salvati ratio 15 was initially less t h a n 1, it r e t u r n e d to normal after the figure-of-eight wire support was removed.
Discussion Patellar t e n d o n rupture after TKA is an uncomm o n event. The most frequently implicated etiologies are (1) attempts to gain wide exposure in a knee with limited m o t i o n Y ,I2,14 (2) distal patellar t e n d o n realignment for patellar dislocation, ~2 (3) implant
Fig. 2. (A) Preoperative lateral radiograph of case 1. Note that the Insall-Salvati ratio is increased. (B) Postoperative lateral radiograph showing the normal position of the patella.
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The Journal ofArthroplasty Vol. 10 No. 3 June 1995
Fig. 3. (A) Preoperative radiograph ol case 2 showing the position of the patella. (B) Postoperative radiograph after repair of the patellar tendon avulsion.
design a n d c o m p o n e n t alignment, 9,17 a n d (4) i m p i n g e m e n t of the prosthesis on the tendon, n Dilferent techniques h a v e b e e n reported in the literature, b u t no one has obtained consistent clinical success. Primary sutures, z7,8,1°,12 staple repair, 4'12 semitendinosus a u g m e n t a t i o n , 11,xz14 plantaris augmentation, 1 distal extensor m e c h a n i s m allograft, 13 carbon-fiber graft, xs'~9 bovine x e n o g r a f t ] 2,2° and expectant t r e a t m e n t w i t h o u t repair a,6,x2 or with extension casting 8 h a v e all yielded m i x e d results. Of 18 knees in a series reported by Rand et al., ~ 16 u n d e r w e n t reconstruction by p r i m a r y suture; however, only 4 (25%) w e r e successful. Two failed repairs w e r e c o n v e r t e d arthrodeses, and one septic case required an a b o v e - k n e e a m p u t a t i o n . In their series of 13 knees, E m e r s o n et al. e m p l o y e d a n e w a n d aggressive technique involving allograft distal extensor m e c h a n i s m reconstruction.13 The composite graft consisted of a quadriceps tendon, a patella with a c e m e n t e d prosthesis, a patellar tendon, a n d a tibial tubercle. Rupture of the quadriceps junction occurred once a n d was resutured, a n d r u p t u r e of the graft occurred on one occasion. Knee extension p o w e r a n d i m p r o v e d function w e r e achieved in the r e m a i n i n g cases, although m i n i m a l extensor lag was present in three cases. Gustillo a n d T h o m p s o n reported on patellar tendon ruptures in two elderly patients w i t h TKA, one of w h o m experienced a r e r u p t u r e after repair, n Both w e r e treated w i t h p r i m a r y sutures that connected the semitendinosus graft to a figure-of-eight wire support. Cadambi a n d Engh treated seven patients using a n a u t o g e n o u s graft of the semitendinosus tendon. 14 Although the semitendinosus graft has only
40 to 50% of the strength of a patellar ligament graft, the patients regained control of quadriceps function a n d extensor strength. Other authors r e c o m m e n d i n g suture or staple repair of the t e n d o n reported consistently p o o r outcomes, ls-20 We h a v e described an easy surgical technique that allows a s h o r t - t e r m r e t u r n of functional extensor power. Both of our patients progressed rapidly with standard rehabilitation p r o g r a m s a n d h a v e retained extensor p o w e r w i t h o u t lag after a followup period of 2 years. Although repair is technically feasible a n d yields good clinical results, in cases w h e r e e x t e n d e d exposure of the k n e e is required, p r e v e n t i o n of a rupture by p l a c e m e n t of a Kirschner wire in the tendon is preferred.
References 1. Wilson FC: Results of knee replacement with Walldius prosthesis: an interim report. Clin Orthop 120:39, 1976 2. Lettin AWF: The Stanmore hinged knee arthroplasty. J Bone Joint Surg 60B:327, 1978 3. Gibbs AN: A comparison of the Freeman-Swanson (ICLI-I) and Walldius prostheses in total knee replacement. J Bone Joint Surg 61B:358, 1979 4. Yamamoto S: Total knee replacement with KodamaYamamoto knee prosthesis. Clin Orthop 145:60, 1979 5. Wilson FC: Results of knee replacement with the Walldius and geometric prostheses: a comparative study. J Bone Joint Surg 62A:497, 1980 6. Kaufer H: Spherocentric arthroplasty of the knee: clinical experience with an average four-year followup. J Bone Joint Surg 63A:545, 1981
PatellarTendonAvulsion
7. Lettin AWF: The long-term results of Stanmore total knee replacements. J Bone Joint Surg 66B:349, 1984 8. Oglesby JW: The evolution of knee arthroplasty with three generations of prostheses. Clin Orthop 186:96, 1984
9. Townley CO: The anatomic total knee resurfacing arthroplasty. Clin Orthop 192:82, 1985 10. Webster DA: Complications of variable axis in total knee arthroplasty. Clin Orthop 193:160, 1985 11. Gustillo R, Thompson R: Quadriceps and patellar tendon ruptures following total knee arthroplasty, p. 41. In Rand JA, Dorr LD (eds): Total arthroplasty of the knee: proceedings of the Knee Society, 1985-1986. Aspen, Rockville, MD, 1987 12. Rand JA, Morrey BF, Bryan RS: Patellar tendon rupture after total knee arthroplasty. Clin Orthop 244:233, 1989 13. Emerson RH Jr, Head WC, Malinin TI: Reconstruction of patellar tendon rupture after total knee arthroplasty with an extensor mechanism allograft. Clin Orthop 260:154, 1990
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14. Cadambi BA, Engh GA: Use of a semitendinosus tendon autogenous graft for rupture of the patellar ligam e n t after total knee arthroplasty. J Bone Joint Surg 74A:974, 1992 15. Insall J, Salvati E: Patella position in the normal knee joint. Radiology 101:101, 1971 16. Bunnell S: The early treatment of h a n d injuries. J Bone Joint Surg 33A:807, 1951 17. Figgie HE: The effect of alignment of the implant in fractures of the patella after condylar total knee arthroplasty. J Bone Joint Surg 71A:1031, 1989 18. Jenkins DHR: The role of flexible carbon-fibre implants as tendon and ligament substitutes in clinical practice: preliminary report. J Bone Joint Surg 62B:497, 1980 19. Keating EM: Use of carbon fiber implant as a knee extensor mechanism replacement in parts: a biomechanical study. Orthop Trans 7:281, 1983 20. A b b i n k EP: P r e l i m i n a r y r e p o r t on the use of xenografts in the knee instability problems. Orthop Trans 7:84, 1983