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Patella position and biomechanical properties of the patellar tendon 1 year after removal of its central third
Clinical Biomechanics Vol. i2. NC. 4, pp. 267-271, 1997 0 1997 Elsevier Science Limited. All rights reserved Printed in Great Britain 026X-0033197$17.00 + 0.00 ELSEVIER
PII: SO268-0033(97)00002-S
Patefla pusition and biomechanical properties of the patellar tendon 1 year after removal of its central third K-F Hanselmann L ClaeS Prof Dr biol Abteilung
Dipl-Biol,
L Diirselen
Dr biol hum,
P Augat
Dr biol hum,
hum
Unfallchirurgische
Forschung
und Biomechanik,
Universitdt
Ulm, Germany
Abstract Objective. The aim of this study was to investigate how the removal of a patellar tendon graft for cruciate ligament reconstruction influences the mechanical properties of the remaining patellar tendon and the position of the patella at the knee joint. Design. The experimental model of this in vivo study was the anterior cruciate ligament reconstruction in sheep. Background. While the efficacy of a patellar tendon third as a ligament replacement has been extensively investigated, the consequences for the function of the remaining tendon and patella position remain unclear. Methods. The central third of the patellar tendon from the right knees of 10 animals was removed for cruciate ligament replacement. One year postoperatively, the position of the patella within the joint and the stiffness and modulus of elasticity of the remaining tendon were compared with the non-operated contralateral controls. Results. The patella position did not change in the operated knee joints in comparison with the controls. The cross-sectional area of the operated patellar tendon increased significantly by scar tissue formation at the defect site. Conclusion. Although the inferior mechanical properties of the scar tissue reduced the modulus of, elasticity of the tendon, the increase in cross-sectional area allowed it to develop a structural stiffness similar to the control tendons. Relevance The central third of the patellar tendon is often used for ligament replacement. Resulting biomechanical and structural changes in the remaining patellartendon have not been pr&viously reported using an in viva animal model. The recovery of the biomechanical properties of the partially resected tendons allows for continued function. @ 1997 Elsevier Science Ltd. Key words: Patella, patellar tendon, biomechanical Clin. Biomech.
Vol. 12, No. 4, 267-271,
properties,
sheep
1997
Introduction Both alloplastic materials’-” and tendon grafts’ have been used for cruciate ligament reconstruction. Reconstruction with a patellar tendon graft is the current standard’-” because of the similar biomechanical properties of tendon and ligament. While the efficacy of the tendon as a ligament replacement has been extensively investigatedlO- l4 the consequences for the function of the remaining tendon and patella position remain unclear. Few investigations have reported the resulting changes at the site of exReceived: 16 February 1995; Accepted: 7 January 1991 Correspondence and reprint requests 10: Dr L Diirselen, Abteihmg Unfallchirurgische Forschung und Biomechanik, Helmholtzstr. 14, IJniversitlt Ufm, 89081 Ulm, Germany
plantation’s,lh. Postoperative complications from tendon grafting are relatively infrequent, although occasionally ruptures of the tendon at the distal pole of the patella are reported “-” . Some authors furthermore, have observed malpositions of the patella as a result of a decrease in patellar tendon length in both clinical studies20-2’ and animal studies23324.In these casesthe tendons are weakened by a decrease in crosssectional area and by degenerative changes such as necrosis. The goal of this study was to determine if partial removal of the patellar tendon for grafting purposes after 1 year results in: (1) a decrease in patellar tendon length and subsequent malposition of the patella; and (2) a decrease in its biomechanical properties.
268
Clin. Biomech.
Vol. 12, No. 4, 1997
Figure 1. Method of lnsall and Salvati (1971) to determine the relation between the patella length (Lp) and the length of the patellar tendon (LpT).
Methods
Ten adult male merino sheep weighing 58 kg (SD 2) underwent cruciate ligament reconstruction. The central one-third of the patellar tendon was harvested and implanted as a substitute for the anterior cruciate ligament in the ipsilateral knee joint5. The tendon defect was closed by three interrupted sutures (Vicryl, Ethicon, Norderstedt, Germany) and loose adaptation of the edges. Animals were allowed full range of motion immediately following the operation. After 1 year the animals were sacrificed. The study was approved by the German Regierungprasidium (Tubingen No. 325) and followed national regulations for the care and use of animals. All skin and muscle tissue were removed from the knee joint while preserving the capsule. To determine the length of the patella (Lr) and patellar tendon (Lm), lateral radiographs were taken (Faxitron, 43805N X-Ray-System, Hewlett Packard, USA) with the joint completely extended by a tensile force of 50 N (simulating a contracted quadriceps muscle) applied to the proximal end of the patella (Figure 1). The patella position quotient, q, defined as length of patella (Lp) over length of patellar tendon (Lrr), was used as a measure of patella position25. Once the dimensions were determined the patella, patellar tendon, and a part of the tuberosity were removed. A gross inspection of the patella concerning cartilage damage and the consistency of the tendon was performed. To determine the cross-sectional areas the
tendons were placed between two angles to obtain a right-angled shape under load. With a caliper the width and the depth of the tendons could be measured. To ensure consistency all measurements were performed by the same person. As the knee joints were used for further investigations on the ACL-replacement, only a fragment of the tuberosity could be used for the tensile test. The patellar tendon was prepared for tensile testing by first embedding the bony insertion sites in methacrylate (Technovit 1040, Kulzer, Homburg, Germany). The embedded ends were *then mounted in a materials testing machine (Type 1445, Zwick, Ulm, Germany). To guarantee better force transmission and to avoid having the specimens slip from the supports, the patella as well as the tuberosity were wrapped with metal tapes. The bony insertions were orientated in the testing mounts until a relatively uniform strain of all tendon fibres was obtained. The tendons were preloaded to 5 N then strained at 50 mm/min to 300 N (Figure 2 (A)). Following an isometric test method, the tendon length was held constant and the load decrease F, during a 3-min stress-relaxation test was recorded (B). Then the load was reduced to 20 N (C) and the specimens were allowed to recover for another 3 min (D). Finally a tensile test to failure (E) was carried out. During the entire testing period the tendons were kept moist with Ringer’s solution. To measure the change in tendon length we used a digital displacement transducer (Type 066510B, Zwick, Ulm, Germany), which was clamped directly to the preloaded tendons. The initial distance between the clamps (L,) was 12 mm. Stiffness was determined from the linear region of the load-extension curve. To calculate modulus of elasticity, extension was normalized to initial patella length to obtain strain and the cross-sectional area divided into load to obtain stress. The patellar tendons from the operated tendons as well as from the controls were cross-sectioned. After fixation in 4% buffered formalin they were embedded in paraffin blocks. Histological cross-sections were taken. The sections were stained with haematoxylin and eosin and examined under polarized light.
z 2 9 !?I z
A
E
A
B
c.
D
E
)
Figure 2. Principal sequence of the tensile test. A, stress; 9.3 min relaxation; C, discharge; D, 3 min recovering; E, tensile test to failure.
TIME
Hanselmann
et al: Biomechanical
properties
of pateilar
269
tendon
Results Patella position and patellar tendon length
After 1 year no significant malposition of the operated patellae was observed. In addition the quotient, q, of the operated knee joints (q = 0.67 (SD 0.07)) was not significantly less than the q of the contralateral controls (q = 0.69 (SD 0.06)). These data indicated that the operated patellar tendon did not shorten. The macroscopic control of the retropatellar cartilage revealed no signs of damage in the operated joints. Although the operated tendons did not shorten, the cross-sectional areas of these tendons markedly increased by inhomogeneous scar tissue formation over the entire region of the initial explanation. Figure 3a demonstrates the collageneous tissue of normal sheep patellar tendon, while on the operated tendons the scar tissue dominates (Figure 3b). Biomechanical parameters
Figure 3. Histological sections of the patellartendons: (a) normal sheep patellar tendons; (b) operated tendons showing scar tissue (polarized light; bar = 50 urn).
For the statistical evaluation the patella position parameter, q, the cross-sectional area, the stiffness, and the modulus of elasticity were compared with the non-operated contralateral tendons. A paired Student’s t test was carried out. The level of significance was set at (II = 0.05. Results are presented as mean & standard deviation.
There was no statistically significant difference in mean stiffness between the operated and the non-operated patellar tendons (operated: 554 (SD 327) N/mm; nonoperated: 605 (SD 345) N/mm; P = 0.38). Since the cross-sectional area of the operated patellar tendons significantly increased (Figure 4; P< O.OS),the moduli of elasticity were much less for the operated tendons compared to the control tendons (Figure 5; P = 0.06). The mean load decrease, F,, measured after 3 min relaxation (relaxation test part B, Figure 2) did not show a significant difference between the operated (100 (SD 31) N) and non-operated tendons (101 (SD 31) N). During the tensile tests failure occurred at the tibia1 insertion sites of the tendons. The tendons themselves did not rupture. Thus, the tensile strength, which varied between 523 and 1884 N for the operated tendons and between 787 and 1793 :N for the nonoperated tendons, are not absolute failure loads of the tendons, but failure loads of the technical fixation in the machine. In this situation the determined failure loads 1200 T Nz 1000 t
2 2 8 2 0 Li 2
OPERATED
NON-OPERATED
Figure 4. Cross-sectional areas of the patellar tendons. The operated tendons show significantly increased cross-sectional areas compared the controls (Pk 0.05).
800 600 400 200 0 OPERATED
to
NON- OPERATED
Figure 5. Moduli of elasticity of the patellar tendons. The modulus elasticity is decreased in the operated tendons (P = 0.06).
of
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Clin. Biomech. Vol. 12, No. 4, 1997
of the operated patellar tendons corresponded to the controls. Discussion Our investigation revealed no indication for a significant change in patellar position or shortening of the patellar tendon at the operated knee joint 1 year postoperatively. These results coincide with the sonographic measurements of Mast et a1.26.The shortening of the patellar tendons as observed by Rehm23 and Kasperczykz4 in sheep is not supported by this study. The average stiffness of the operated patellar tendons was not significantly different from the controls 1 year postoperatively. This result compares well with one of the few other investigations evaluating the biomechanical properties of the remaining patellar tendon after ligament reconstruction in dogs*‘. The almost complete regeneration of the stiffness of the operated tendon after 1 year contrasts with lower stiffness measurements after 6 months observed by Burks et a1.15.These findings suggest that the healing process is not yet finished after 6 months. Since the operated tendon heals, the considerable increase in cross-sectional area was gained by. replacing the removal site with biomechanically poor scar tissue. An increase in cross-sectional area compared to the control tendon is necessary for comparable stiffness to be achieved*s. The larger cross-section of the operated tendons also seemed to preserve their viscoelastic properties since the load decrease measured during the stress relaxation test did not reveal a difference between operated and control tendons. In this study the patellar tendons could not be strained to failure because of insufficient fixation of the tuberosity, despite reinforcement with metal tapes. Therefore the determined mean failure loads do not represent the true strengths of the tendons. In a few caseswhere a better fixation could be achieved the data of the operated patellar tendons, as well as the data of the controls, are comparable to the data found by other authors’6324. So it seems that apart from the stiffness the ultimate strain has regenerated 1 year postoperatively and that effectively there may be only material rather than functional differences remaining. Closing the tendon defect using only a few single sutures and slight adaptation did not result in a shortening of the tendon or in cartilage destruction. In other sheep experiments the entire defect was enclosed with uninterrupted suture 24. After 1 year the patellar tendon was shortened. Other authors have suggested keeping the defect completely open to avoid tendon shortening 15,29,30 . A regeneration of the biomechanical properties of the partially resected tendon occurs for the stiffness and probably for failure loads. The rebuilt tissue is scar
tissue, which is of minor quality with a lower elastic modulus, and is not replaced by normal tendon tissue after 1 year. In summary, there is no change in the sheep’s patella position by the removal of a tendon graft for ligament reconstruction. The recovery of the biomechanical properties of the partially resected tendons to the controls allows for its continued function.
References 1. Grood, E. S. and Noyes, F. R. Cruciate ligament prosthesis: strength, creep and fatigue properties. Journal of Bone and Joint Surgery, 1976,58A(8),
1083-1088. 2. Kennedy, J. C. Application of prosthetics to anterior cruciate ligament reconstruction and repair. Clinical Orthopaedics, 1983, 172, 125-128. 3. Alm, A. and Gillquist, J. Reconstruction of the anterior cruciate ligament by using the medial third of the patellar ligament. Acta Chir Stand, 1974,140,289-296. 4. Jenkins, D. H. R. The repair of cruciate ligaments with flexible carbon fibre. Journal of Bone and Joint Surgery, 1978,6OB, 520-522. 5. Clancy, W. G., Narechania, R. G., Rosenberg, T. D. et al. Anterior and posterior cruciate ligament reconstruction in rhesus monkeys. Journal of Bone and Joint Surgery, 1981,63A(8), 1270-1283. 6. Drez, D. J., DeLee J., Holden, J. P. et al. Anterior cruciate ligament reconstruction usingbone-patellar tendon-allografts. American Journal of Sports Medicine, 1991,19(3), 256-263. 7. Jones, K. G. Reconstruction of the anterior cruciate ligament using the central one-third of the patellar ligament. Journal of Bone and Joint Surgery, 1970, 52A(7), 1302-1308. 8. Jones, K. G. Results of use of the central one-third of the patellar ligament to compensate for anterior cruciate ligament deficiency. Clinical Orthopaedics, 1980,147, 39-44. 9. Noyes, F. R., Butler, D. L., Grood, E. S. et al. Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstruction. Journal of Bone and Joint Surgery, 1984,66A, 344-352. 10. Arnoczky, S. P., Tarvin, G. B. and Marshall, J. L. Anterior cruciate ligament replacement using patellar tendon. An evaluation of graft revascularization in the dog. Journal of Bone and Joint Surgery, 1982, &IA, 217-224. 11. Clancy, W. G., Nelson, D. A., Reider, B. and Narechania, R. G. Anterior cruciate ligament reconstruction using one-third of the patellar ligament, augmented by extra-articular tendon transfers. Journal of Bone and Joint Surgery, 1982,64A, 352-359. 12. Graf, B. and Uhr, F. Complications of intra-articular cruciate reconstruction. Clinical Sports Medicine, 1988, 7,835-848. 13. Kasperczyk, W. J., Bosch, U., Oestern, H. J. and Tscherne, H. Bedeutung der Rekonstruktion des hinteren Kreuzbandes fiir das Kniegelenk - Stabilitat und Knorpelveranderungen im Tiermodell tiber zwei Jahre. Chirurgisches Forum, 1991,241-246. 14. Paterson, F. W. N. and Trickey, E. L. Anterior cruciate ligament reconstruction using part of the patellar tendon as a free graft. Journal of Bone and Joint Surgery, 1986, 68(3), 453-457.
Hanselmann
15. Burks, R. T., Haut, R. C. and Lancaster, R. L. Biomechanical and histological observations of the dog patellar tendon after removal of its central third. American Journalof Sports Medicine, 1990,18(2), 146-153. 16. Scherer, M. A., Fruh, H.-J., Ascherl, R. and Siebels, W. Biomechanische Untersuchungen zur Veranderung der Patellarsehne nach Transplantatentnahme. Aktuelle Traumatologie, 1993,23, 129-132. 17. Bonamo, J. J., Krinick, R. M. and Sporn, A. A. Rupture of the patellar ligament after use of its central third for cruciate reconstruction. Journal of Bone and Joint Surgery, 1984,66A, 1294-1297. 18. Langan, P., Fontanetta, A. P. Rupture of the patellar tendon after use of its central third. Orthopaedic Review, 1987, 16(5), 317-321. 19. Wallenbock, E. Rupture of the patellar ligament - a late sequela after removal of a bone-tendon-bone graft as cruciate ligament substitute. Langenbecks Archiv Fur Chirurgie, 1993,378(6), 39-340. 20. O’Brian, S. J., Warren, R. F., Pavlov, H. et al. Reconstruction of the chronically insufficient anterior cruciate ligament with the central third of the patellar ligament. Journal of Bone and Joint Surgery, 1991, 73A(2), 278-286.
21. Paulos, L. E., Rosenberg, T. D., Drawbert, J. et al. Infrapatellar contracture syndrome. An unrecognized cause of knee stiffness with patella entrapment and patella infera. American Journal of Sports Medicine. 1987,15(4), 331-341. 22. Wojtys, E. M. and Gikas, P. Patella baja syndrome. AAOS 53. Annual Meeting. New Orleans, 20-2.5 February 1986.
et al: Biomechanical
properties
of patellar
tendon
271
23. Rehm, K. E. and Holzmuller, W. Patellarsehnenverkiirzung nach Transplantatentnahme. Unfallheilkunde,
1990,212,453-454.
24. Kasperczyk, W., Bosch, U., Rosacha, S. and Oestern, H. J. Die Patellarsehne nach Transplantatentnahme zur Kreuzbandrekonstruktion - Eine tierexperimentelle biomechanische Studie. Unfallheilkunde,
1989,207,287-288.
25. Insall, J. and Salvati, E. Patella position in the normal knee joint. Radiology, 1971, 101, 101-104. 26. Mast, R., Neubert, M. and Steinbriick, K. Sonographische und klinische Befunde am Ligamenturn patellae nach Entnahme des mittleren Drittels zur Kreuzbandersatzplastik. Sportverletzung-Sportschaden, 1991,5,199-201. 27. Cabaud. E. H., Feagin, J. A. and Rodkey, W. G. Acute anterior cruciate ligament injury and augmented repair. American Journal of Sports Medicine, 1980,8(6), 395-401. 28. Holzmuller, W., Rehm, K. E., Perren, S. M. and Ecke, H. Schwacht die Jones-Plastik die Patellarsehne? Unfallheilkunde, 1989,207,278. 29. Berg, E. E. Intrinsic healing of the patellar tendon donor site defect after anterior cruciate ligament reconstruction. Clinical Orthopaedics, 1092. 278, 160- 163. 30. Cerullo, G.,.Puddu, G., Gianni E. et al. Anterior cruciate ligament patellar reconstruction: it is probably better to leave the tendon defect open. Knee Surgery, Sports Traumatology
14- 17.
and Arthroscopy.
1995,3,
PII: SO268-0033(97)00002-S
Patefla pusition and biomechanical properties of the patellar tendon 1 year after removal of its central third K-F Hanselmann L ClaeS Prof Dr biol Abteilung
Dipl-Biol,
L Diirselen
Dr biol hum,
P Augat
Dr biol hum,
hum
Unfallchirurgische
Forschung
und Biomechanik,
Universitdt
Ulm, Germany
Abstract Objective. The aim of this study was to investigate how the removal of a patellar tendon graft for cruciate ligament reconstruction influences the mechanical properties of the remaining patellar tendon and the position of the patella at the knee joint. Design. The experimental model of this in vivo study was the anterior cruciate ligament reconstruction in sheep. Background. While the efficacy of a patellar tendon third as a ligament replacement has been extensively investigated, the consequences for the function of the remaining tendon and patella position remain unclear. Methods. The central third of the patellar tendon from the right knees of 10 animals was removed for cruciate ligament replacement. One year postoperatively, the position of the patella within the joint and the stiffness and modulus of elasticity of the remaining tendon were compared with the non-operated contralateral controls. Results. The patella position did not change in the operated knee joints in comparison with the controls. The cross-sectional area of the operated patellar tendon increased significantly by scar tissue formation at the defect site. Conclusion. Although the inferior mechanical properties of the scar tissue reduced the modulus of, elasticity of the tendon, the increase in cross-sectional area allowed it to develop a structural stiffness similar to the control tendons. Relevance The central third of the patellar tendon is often used for ligament replacement. Resulting biomechanical and structural changes in the remaining patellartendon have not been pr&viously reported using an in viva animal model. The recovery of the biomechanical properties of the partially resected tendons allows for continued function. @ 1997 Elsevier Science Ltd. Key words: Patella, patellar tendon, biomechanical Clin. Biomech.
Vol. 12, No. 4, 267-271,
properties,
sheep
1997
Introduction Both alloplastic materials’-” and tendon grafts’ have been used for cruciate ligament reconstruction. Reconstruction with a patellar tendon graft is the current standard’-” because of the similar biomechanical properties of tendon and ligament. While the efficacy of the tendon as a ligament replacement has been extensively investigatedlO- l4 the consequences for the function of the remaining tendon and patella position remain unclear. Few investigations have reported the resulting changes at the site of exReceived: 16 February 1995; Accepted: 7 January 1991 Correspondence and reprint requests 10: Dr L Diirselen, Abteihmg Unfallchirurgische Forschung und Biomechanik, Helmholtzstr. 14, IJniversitlt Ufm, 89081 Ulm, Germany
plantation’s,lh. Postoperative complications from tendon grafting are relatively infrequent, although occasionally ruptures of the tendon at the distal pole of the patella are reported “-” . Some authors furthermore, have observed malpositions of the patella as a result of a decrease in patellar tendon length in both clinical studies20-2’ and animal studies23324.In these casesthe tendons are weakened by a decrease in crosssectional area and by degenerative changes such as necrosis. The goal of this study was to determine if partial removal of the patellar tendon for grafting purposes after 1 year results in: (1) a decrease in patellar tendon length and subsequent malposition of the patella; and (2) a decrease in its biomechanical properties.
268
Clin. Biomech.
Vol. 12, No. 4, 1997
Figure 1. Method of lnsall and Salvati (1971) to determine the relation between the patella length (Lp) and the length of the patellar tendon (LpT).
Methods
Ten adult male merino sheep weighing 58 kg (SD 2) underwent cruciate ligament reconstruction. The central one-third of the patellar tendon was harvested and implanted as a substitute for the anterior cruciate ligament in the ipsilateral knee joint5. The tendon defect was closed by three interrupted sutures (Vicryl, Ethicon, Norderstedt, Germany) and loose adaptation of the edges. Animals were allowed full range of motion immediately following the operation. After 1 year the animals were sacrificed. The study was approved by the German Regierungprasidium (Tubingen No. 325) and followed national regulations for the care and use of animals. All skin and muscle tissue were removed from the knee joint while preserving the capsule. To determine the length of the patella (Lr) and patellar tendon (Lm), lateral radiographs were taken (Faxitron, 43805N X-Ray-System, Hewlett Packard, USA) with the joint completely extended by a tensile force of 50 N (simulating a contracted quadriceps muscle) applied to the proximal end of the patella (Figure 1). The patella position quotient, q, defined as length of patella (Lp) over length of patellar tendon (Lrr), was used as a measure of patella position25. Once the dimensions were determined the patella, patellar tendon, and a part of the tuberosity were removed. A gross inspection of the patella concerning cartilage damage and the consistency of the tendon was performed. To determine the cross-sectional areas the
tendons were placed between two angles to obtain a right-angled shape under load. With a caliper the width and the depth of the tendons could be measured. To ensure consistency all measurements were performed by the same person. As the knee joints were used for further investigations on the ACL-replacement, only a fragment of the tuberosity could be used for the tensile test. The patellar tendon was prepared for tensile testing by first embedding the bony insertion sites in methacrylate (Technovit 1040, Kulzer, Homburg, Germany). The embedded ends were *then mounted in a materials testing machine (Type 1445, Zwick, Ulm, Germany). To guarantee better force transmission and to avoid having the specimens slip from the supports, the patella as well as the tuberosity were wrapped with metal tapes. The bony insertions were orientated in the testing mounts until a relatively uniform strain of all tendon fibres was obtained. The tendons were preloaded to 5 N then strained at 50 mm/min to 300 N (Figure 2 (A)). Following an isometric test method, the tendon length was held constant and the load decrease F, during a 3-min stress-relaxation test was recorded (B). Then the load was reduced to 20 N (C) and the specimens were allowed to recover for another 3 min (D). Finally a tensile test to failure (E) was carried out. During the entire testing period the tendons were kept moist with Ringer’s solution. To measure the change in tendon length we used a digital displacement transducer (Type 066510B, Zwick, Ulm, Germany), which was clamped directly to the preloaded tendons. The initial distance between the clamps (L,) was 12 mm. Stiffness was determined from the linear region of the load-extension curve. To calculate modulus of elasticity, extension was normalized to initial patella length to obtain strain and the cross-sectional area divided into load to obtain stress. The patellar tendons from the operated tendons as well as from the controls were cross-sectioned. After fixation in 4% buffered formalin they were embedded in paraffin blocks. Histological cross-sections were taken. The sections were stained with haematoxylin and eosin and examined under polarized light.
z 2 9 !?I z
A
E
A
B
c.
D
E
)
Figure 2. Principal sequence of the tensile test. A, stress; 9.3 min relaxation; C, discharge; D, 3 min recovering; E, tensile test to failure.
TIME
Hanselmann
et al: Biomechanical
properties
of pateilar
269
tendon
Results Patella position and patellar tendon length
After 1 year no significant malposition of the operated patellae was observed. In addition the quotient, q, of the operated knee joints (q = 0.67 (SD 0.07)) was not significantly less than the q of the contralateral controls (q = 0.69 (SD 0.06)). These data indicated that the operated patellar tendon did not shorten. The macroscopic control of the retropatellar cartilage revealed no signs of damage in the operated joints. Although the operated tendons did not shorten, the cross-sectional areas of these tendons markedly increased by inhomogeneous scar tissue formation over the entire region of the initial explanation. Figure 3a demonstrates the collageneous tissue of normal sheep patellar tendon, while on the operated tendons the scar tissue dominates (Figure 3b). Biomechanical parameters
Figure 3. Histological sections of the patellartendons: (a) normal sheep patellar tendons; (b) operated tendons showing scar tissue (polarized light; bar = 50 urn).
For the statistical evaluation the patella position parameter, q, the cross-sectional area, the stiffness, and the modulus of elasticity were compared with the non-operated contralateral tendons. A paired Student’s t test was carried out. The level of significance was set at (II = 0.05. Results are presented as mean & standard deviation.
There was no statistically significant difference in mean stiffness between the operated and the non-operated patellar tendons (operated: 554 (SD 327) N/mm; nonoperated: 605 (SD 345) N/mm; P = 0.38). Since the cross-sectional area of the operated patellar tendons significantly increased (Figure 4; P< O.OS),the moduli of elasticity were much less for the operated tendons compared to the control tendons (Figure 5; P = 0.06). The mean load decrease, F,, measured after 3 min relaxation (relaxation test part B, Figure 2) did not show a significant difference between the operated (100 (SD 31) N) and non-operated tendons (101 (SD 31) N). During the tensile tests failure occurred at the tibia1 insertion sites of the tendons. The tendons themselves did not rupture. Thus, the tensile strength, which varied between 523 and 1884 N for the operated tendons and between 787 and 1793 :N for the nonoperated tendons, are not absolute failure loads of the tendons, but failure loads of the technical fixation in the machine. In this situation the determined failure loads 1200 T Nz 1000 t
2 2 8 2 0 Li 2
OPERATED
NON-OPERATED
Figure 4. Cross-sectional areas of the patellar tendons. The operated tendons show significantly increased cross-sectional areas compared the controls (Pk 0.05).
800 600 400 200 0 OPERATED
to
NON- OPERATED
Figure 5. Moduli of elasticity of the patellar tendons. The modulus elasticity is decreased in the operated tendons (P = 0.06).
of
270
Clin. Biomech. Vol. 12, No. 4, 1997
of the operated patellar tendons corresponded to the controls. Discussion Our investigation revealed no indication for a significant change in patellar position or shortening of the patellar tendon at the operated knee joint 1 year postoperatively. These results coincide with the sonographic measurements of Mast et a1.26.The shortening of the patellar tendons as observed by Rehm23 and Kasperczykz4 in sheep is not supported by this study. The average stiffness of the operated patellar tendons was not significantly different from the controls 1 year postoperatively. This result compares well with one of the few other investigations evaluating the biomechanical properties of the remaining patellar tendon after ligament reconstruction in dogs*‘. The almost complete regeneration of the stiffness of the operated tendon after 1 year contrasts with lower stiffness measurements after 6 months observed by Burks et a1.15.These findings suggest that the healing process is not yet finished after 6 months. Since the operated tendon heals, the considerable increase in cross-sectional area was gained by. replacing the removal site with biomechanically poor scar tissue. An increase in cross-sectional area compared to the control tendon is necessary for comparable stiffness to be achieved*s. The larger cross-section of the operated tendons also seemed to preserve their viscoelastic properties since the load decrease measured during the stress relaxation test did not reveal a difference between operated and control tendons. In this study the patellar tendons could not be strained to failure because of insufficient fixation of the tuberosity, despite reinforcement with metal tapes. Therefore the determined mean failure loads do not represent the true strengths of the tendons. In a few caseswhere a better fixation could be achieved the data of the operated patellar tendons, as well as the data of the controls, are comparable to the data found by other authors’6324. So it seems that apart from the stiffness the ultimate strain has regenerated 1 year postoperatively and that effectively there may be only material rather than functional differences remaining. Closing the tendon defect using only a few single sutures and slight adaptation did not result in a shortening of the tendon or in cartilage destruction. In other sheep experiments the entire defect was enclosed with uninterrupted suture 24. After 1 year the patellar tendon was shortened. Other authors have suggested keeping the defect completely open to avoid tendon shortening 15,29,30 . A regeneration of the biomechanical properties of the partially resected tendon occurs for the stiffness and probably for failure loads. The rebuilt tissue is scar
tissue, which is of minor quality with a lower elastic modulus, and is not replaced by normal tendon tissue after 1 year. In summary, there is no change in the sheep’s patella position by the removal of a tendon graft for ligament reconstruction. The recovery of the biomechanical properties of the partially resected tendons to the controls allows for its continued function.
References 1. Grood, E. S. and Noyes, F. R. Cruciate ligament prosthesis: strength, creep and fatigue properties. Journal of Bone and Joint Surgery, 1976,58A(8),
1083-1088. 2. Kennedy, J. C. Application of prosthetics to anterior cruciate ligament reconstruction and repair. Clinical Orthopaedics, 1983, 172, 125-128. 3. Alm, A. and Gillquist, J. Reconstruction of the anterior cruciate ligament by using the medial third of the patellar ligament. Acta Chir Stand, 1974,140,289-296. 4. Jenkins, D. H. R. The repair of cruciate ligaments with flexible carbon fibre. Journal of Bone and Joint Surgery, 1978,6OB, 520-522. 5. Clancy, W. G., Narechania, R. G., Rosenberg, T. D. et al. Anterior and posterior cruciate ligament reconstruction in rhesus monkeys. Journal of Bone and Joint Surgery, 1981,63A(8), 1270-1283. 6. Drez, D. J., DeLee J., Holden, J. P. et al. Anterior cruciate ligament reconstruction usingbone-patellar tendon-allografts. American Journal of Sports Medicine, 1991,19(3), 256-263. 7. Jones, K. G. Reconstruction of the anterior cruciate ligament using the central one-third of the patellar ligament. Journal of Bone and Joint Surgery, 1970, 52A(7), 1302-1308. 8. Jones, K. G. Results of use of the central one-third of the patellar ligament to compensate for anterior cruciate ligament deficiency. Clinical Orthopaedics, 1980,147, 39-44. 9. Noyes, F. R., Butler, D. L., Grood, E. S. et al. Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstruction. Journal of Bone and Joint Surgery, 1984,66A, 344-352. 10. Arnoczky, S. P., Tarvin, G. B. and Marshall, J. L. Anterior cruciate ligament replacement using patellar tendon. An evaluation of graft revascularization in the dog. Journal of Bone and Joint Surgery, 1982, &IA, 217-224. 11. Clancy, W. G., Nelson, D. A., Reider, B. and Narechania, R. G. Anterior cruciate ligament reconstruction using one-third of the patellar ligament, augmented by extra-articular tendon transfers. Journal of Bone and Joint Surgery, 1982,64A, 352-359. 12. Graf, B. and Uhr, F. Complications of intra-articular cruciate reconstruction. Clinical Sports Medicine, 1988, 7,835-848. 13. Kasperczyk, W. J., Bosch, U., Oestern, H. J. and Tscherne, H. Bedeutung der Rekonstruktion des hinteren Kreuzbandes fiir das Kniegelenk - Stabilitat und Knorpelveranderungen im Tiermodell tiber zwei Jahre. Chirurgisches Forum, 1991,241-246. 14. Paterson, F. W. N. and Trickey, E. L. Anterior cruciate ligament reconstruction using part of the patellar tendon as a free graft. Journal of Bone and Joint Surgery, 1986, 68(3), 453-457.
Hanselmann
15. Burks, R. T., Haut, R. C. and Lancaster, R. L. Biomechanical and histological observations of the dog patellar tendon after removal of its central third. American Journalof Sports Medicine, 1990,18(2), 146-153. 16. Scherer, M. A., Fruh, H.-J., Ascherl, R. and Siebels, W. Biomechanische Untersuchungen zur Veranderung der Patellarsehne nach Transplantatentnahme. Aktuelle Traumatologie, 1993,23, 129-132. 17. Bonamo, J. J., Krinick, R. M. and Sporn, A. A. Rupture of the patellar ligament after use of its central third for cruciate reconstruction. Journal of Bone and Joint Surgery, 1984,66A, 1294-1297. 18. Langan, P., Fontanetta, A. P. Rupture of the patellar tendon after use of its central third. Orthopaedic Review, 1987, 16(5), 317-321. 19. Wallenbock, E. Rupture of the patellar ligament - a late sequela after removal of a bone-tendon-bone graft as cruciate ligament substitute. Langenbecks Archiv Fur Chirurgie, 1993,378(6), 39-340. 20. O’Brian, S. J., Warren, R. F., Pavlov, H. et al. Reconstruction of the chronically insufficient anterior cruciate ligament with the central third of the patellar ligament. Journal of Bone and Joint Surgery, 1991, 73A(2), 278-286.
21. Paulos, L. E., Rosenberg, T. D., Drawbert, J. et al. Infrapatellar contracture syndrome. An unrecognized cause of knee stiffness with patella entrapment and patella infera. American Journal of Sports Medicine. 1987,15(4), 331-341. 22. Wojtys, E. M. and Gikas, P. Patella baja syndrome. AAOS 53. Annual Meeting. New Orleans, 20-2.5 February 1986.
et al: Biomechanical
properties
of patellar
tendon
271
23. Rehm, K. E. and Holzmuller, W. Patellarsehnenverkiirzung nach Transplantatentnahme. Unfallheilkunde,
1990,212,453-454.
24. Kasperczyk, W., Bosch, U., Rosacha, S. and Oestern, H. J. Die Patellarsehne nach Transplantatentnahme zur Kreuzbandrekonstruktion - Eine tierexperimentelle biomechanische Studie. Unfallheilkunde,
1989,207,287-288.
25. Insall, J. and Salvati, E. Patella position in the normal knee joint. Radiology, 1971, 101, 101-104. 26. Mast, R., Neubert, M. and Steinbriick, K. Sonographische und klinische Befunde am Ligamenturn patellae nach Entnahme des mittleren Drittels zur Kreuzbandersatzplastik. Sportverletzung-Sportschaden, 1991,5,199-201. 27. Cabaud. E. H., Feagin, J. A. and Rodkey, W. G. Acute anterior cruciate ligament injury and augmented repair. American Journal of Sports Medicine, 1980,8(6), 395-401. 28. Holzmuller, W., Rehm, K. E., Perren, S. M. and Ecke, H. Schwacht die Jones-Plastik die Patellarsehne? Unfallheilkunde, 1989,207,278. 29. Berg, E. E. Intrinsic healing of the patellar tendon donor site defect after anterior cruciate ligament reconstruction. Clinical Orthopaedics, 1092. 278, 160- 163. 30. Cerullo, G.,.Puddu, G., Gianni E. et al. Anterior cruciate ligament patellar reconstruction: it is probably better to leave the tendon defect open. Knee Surgery, Sports Traumatology
14- 17.
and Arthroscopy.
1995,3,