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Anterior knee pain after anterior cruciate ligament reconstruction could be caused by distinct changes in the patellofemoral alignment.


Normal function of the patellofemoral joint depends on the interaction of several elements including the patellofemoral alignment, bony and soft tissue stability, and muscular interaction. Patellofemoral disorders encompass a wide range of conditions from anterior knee pain to arthrosis. Considering the patellofemoral joint is a subtle system, minor changes in the soft tissue alignment may lead to disturbed patellofemoral interaction. There are several reports claiming that the patellar tendon shrinks a certain percentage after ACL reconstruction (1-3). One paper associates this shortening with anterior knee pain (3). Furthermore, Shino et al. (4) reported deteriorative changes of the patellofemoral articular surfaces after ACL reconstruction. These changes were detected, at a second-look arthroscopy, with an incidence of 44% for ACL reconstruction using allografts and an incidence of 57% using autografts. Hsieh et al (5) recently showed in a cadaver model, that the removal of the ACL led to significant changes of the lateral patellar tilt and lateral patellar shift during knee motion. However, none of the mentioned studies (1-5) investigated possible changes of the patellar alignment after ACL reconstruction as a result of scarring and contracture of the patellar tendon with obvious changes after the development of an infrapatellar contracture syndrome, as described by Paulos et al (2, 6), but with maybe more subtle alterations in patients without arthrofibrosis.

Aim of this study was to investigate the influence of harvesting the central third of the patellar tendon in comparison with the multiple suture repair ACL reconstruction on both the lateral patellofemoral and the Merchant´s angles.


Between 1993 and 1994 patients operated upon because of an ACL deficiency were included in the study. The inclusion criteria were: 1.) informed consent of additional radiograms, 2.) an isolated ACL tear, 3.) no history of patellofemoral problems 4.) radiological confirmation of a normal patella and patellofemoral joint 5) no former knee operations, and 6) free range of motion and no failure of the ACL reconstruction at follow-up. All knees were arthroscopically evaluated and any internal derangements were treated before ACL reconstruction. When the ACL tear was not older than two weeks, high proximal ruptures of the ACL were repaired in the technique described by Marshall et al. (7), using a mini-arthrotomy on the medial side of the patellar tendon (GROUP A). All other ACL tears were reconstructed with the central third of the patellar tendon as a bone tendon bone graft (8) (GROUP B). The gap in the patellar tendon after harvest was not closed. The osseous defects at the patellar apex and tibial tuberosity were filled with spongious bone obtained from the shaping of the bone blocks. Thirty patients underwent ACL reconstruction within six weeks postinjury, and sixteen patients were operated six weeks or more postinjury. The ACL repairs (A) and the ACL grafts (B) were augmented with the synthetic augmentation device (Ligament Augmentation Device: LAD™, 3M, St. Paul, Minnesota) which was led "over the top", and fixed in a rigid double-end fixation technique with a preload of 8 kilopond, with the knee fully extended (9).

Postoperatively, the knee was braced (Donjoy® Smith & Nephew, Carlsbad, CA, USA) at 20° for the first five days after which free range of motion was encouraged. Continuous passive motion (0-0-90° CPM) was performed starting from the first postoperative day for 4 to 6 hours per day. Weight-bearing was allowed as tolerated. Local cryotherapy with cool-packs was issued and nonsteroidal anti-inflammatory drugs were prescribed. Patients were discharged from the hospital on the fourth or fifth postoperative day. Training for competitive sports was allowed after 3 to 4 months, when the thigh circumference returned to the contralateral level.

Patients were asked to come in for a follow-up investigation approximately one year after the ACL reconstruction. The investigations performed included clinical examination, subjective symptoms, and radiographic control. Range of motion was measured with an international standard goniometer. Passive sagital knee laxity was measured with the KT 1000® (MEDmetric, San Diego, California), as described by Daniel et al (10). Preoperatively and at follow-up, radiograms were taken as described by Merchant et al. (11) except that the knee was flexed to 25°, not 45°. Care was taken to keep the axis of the patient’s forefoot vertical. On these radiograms the sulcus angle, the lateral patellofemoral angle (a) (12) and the Merchant congruence angle (b) (11) were measured (Figure 1). The length of the patella and the patellar tendon were measured, as described by Insall and Salvati (13) on lateral radiographs taken in the supine position with the knee flexed to 60°. The patellar vertical height ratio (VHR) was then calculated by dividing the length of the patellar tendon by the length of the patella (Figure 2). The recorded angles and the patella height were statistically compared using an analysis of covariance. A p-value of less than 0.05 was considered statistically significant. 


In group A there were thirteen men and ten women, in group B twelve men and eleven women. The mean age was 26.1 years (±7.8 years) with no significant difference between the two groups. All patients had stable knees with a free range of motion at follow-up.

There were no significant differences, neither preoperatively nor postoperatively, between sulcus angles or between the lateral patellofemoral angles (a) of both groups. (Table 1)

For the Merchant congruence angle (b), significant differences were observed between the preoperatively and the postoperatively recorded values, as well as between Group A and B postoperatively. The mean difference between the preoperatively and postoperatively recorded angles was -1.7 ± 0.9 degrees in Group A, and -4.7 ±0.7 degrees in Group B (p = 0.001). (Table 2)

No significant difference was detected between the groups for the alterations of the patellar tendon length (p=0.9). However, there was a significant decrease from the preoperative measurements to the follow-up investigation (p=0.04). (Table 3)


We investigated the influence of ACL surgery on the patellofemoral joint. Therefore, two techniques for ACL reconstruction, the patellar tendon grafting and the multiple suture repair, were compared in order to measure the patellar alignment on radiograms. Despite the advantages of the use of the central third of the patellar tendon, there are also some drawbacks. In conjunction with donor-site morbidity, another possible major risk is an increase of the incidence of patellofemoral arthrosis. The high occurrence of anterior knee pain cannot be explained solely by donor-site morbidity, as it occurs in a comparable percentage even after the use of hamstring tendons for ACL reconstruction (14).

Recently, Hsieh et al (5) reported a cadaver study with significant effects of the removal of the ACL on patellar kinematics, which returned to normal after ACL reconstruction. They stated that one limitation was that their study could not address the healing process, which could alter the pressure distribution as a result of scarring and contracture of the patellar tendon. Our results indicate a definite influence of the graft harvest on the patellofemoral joint. Care was taken to use the same anatomic landmarks when taking the measurements. As no significant differences were recorded for the sulcus angle between the preoperative and follow-up radiographs, it can be assumed that the radiographs were taken very carefully and persistently in the same position. The lateral patellofemoral angle did not differ after the ACL reconstruction. However, the Merchant’s angle showed a significant decrease on the follow-up radiographs. One could argue that these changes are minimal. Although no pathologic angles were measured, neither preoperatively nor at follow-up, the exactness of the measurements give reason to believe that a change of approximately 5° can not be explained by inaccuracy. This change is a hint of a distinct alteration in the patellofemoral alignment. However, the ACL deficiency could have caused a change of the patellofemoral alignment by itself, but the authors do not believe that the ACL deficiency preoperatively significantly influenced the results, as the in Group A no significant change of the measured angles occurred at follow-up and all knees included were stable.

Changes in the patellar height, results in different mechanical forces acting on the patellofemoral joint. The change of the patella height can not be the only explanation for significant differences of the Merchant angle between Groups A and B, as this study as well as an investigation with more than 100 patients showed that changes of the patella height were the same regardless the operation procedure (ACL repair vs. ACL grafting, unpublished data). The extracted patellar tendon graft, not located exactly in the center, or the scar formation, not conducting forces as the original tendon, could be an explanation for the medial migration of the patella.

This study was performed without the benefit of accelerated rehabilitation. The above cited papers which describe high rates of anterior knee pain were also performed without accelerated rehabilitation (2, 3, 15, 16). When we began to accelerate the rehabilitation program, the rate of anterior knee pain in our patients dropped down and even without postoperative fixation no adverse effects were seen (17). This also supports the concept of patellar tendon shrinkage being one major responsible factor for the changes in the patellofemoral alignment and subsequently anterior knee pain.

Donor site morbidity cannot be the only explanation for the arthroscopic finding of deteriorate changes around the central ridge of the patella (4) and the frequent occurrence of anterior knee pain after ACL reconstruction (2, 3, 15, 16). Furthermore, it is probably justifiable to hypothesize that graft harvest and/or scar formations influence the patellar alignment. As the scaring must not be limited to the site of the graft harvest, but can be also generalized, like an infrapatellar contracture syndrome (2), these distinct aspects must likewise be taken into consideration when the patient complains about anterior knee pain after ACL reconstruction, without presenting a completely infrapatellar contracture syndrome.


Presented in part at the 2nd Patellofemoral Study Group Meeting in Interlaken, Switzerland, 1996.


1. Dandy DJ, Desai SS. Patellar tendon length after anterior cruciate ligament reconstruction. J Bone Joint Surg (1994);76B :198-99

2. Paulos LE, Rosenberg TD, Drawbert J, et al. Infrapatellar contracture syndrom: an unrecognized cause of knee stiffness with patella entrapment and patella infera.  Am J Sports Med (1987);15:331-341

3. O´Brien SJ, Warren RF, Pavlov H, Panariello R, Wickiewicz TL. Reconstruction of the chronically insufficient anterior cruciate ligament with the central third of the patellar ligament. J Bone Joint Surg (1991);73 A:278-86

4. Shino K, Nakagawa S, Inoue M, Horibe S, Yoneda M. Deterioration of patellofemoral articular surfaces after anterior cruciate ligament reconstruction. Am J Sports Med (1993);21:206-211

5. Hsieh Y-F, Draganich LF, Ho SH, Reider B. The effects of removal and reconstruction of the anterior cruciate ligament on patellofemoral kinematics. Am J Sports Med (1998);26:201-209

6. Paulos LE, Wnorowski DC, Greenwald AE. Infrapatellar contracture syndrome diagnosis, treatment, and long term follow up. Am J Sports Med (1994);22:440-9

7. Marshall JL, Warren RF, Wickiewicz TL, Reider B. The anterior cruciate ligament: A technique of repair and reconstruction. Clin. Orthop (1979);143:97

8. Clancy WGJr, Nelson DA, Reider B. Anterior cruciate ligament reconstruction using one third of the patellar ligament, augmented by extra-articular tendon transfers. J. Bone Joint Surg (1982);64 A:352-35

9. Schabus R. Die Bedeutung der Augmentation für die Rekonstruktion des vorderen Kreuzbandes. Acta Chir. Austriaca (1988);76-Suppl.:1-48

10. Daniel DM, Malcom LL, Losse G, Stone ML, Sachs R, Burks R. Instrumented measurement of anterior laxity of the knee. J Bone Joint Surg (1985);67A:720-726

11. Merchant AC, Mercer RL, Jacobson RH, Cool CR. Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg (1974);56A:1391-1396

12. Laurin CA, Dussault R, Levesque HP. The tangential x-ray investigation of the patellofemoral joint: X-ray technique, diagnostic criteria, and their interpretation. Clin Orthop (1979);144:16-26

13. Insall JN, Salvati E. Patella position in the normal knee joint. Radiology (1971);101:101-4

14. McKernan DJ, Paulos LE (1994) in Knee Surgery Fu FH, Harner CD,  Vince KG, Eds. (Williams and Wilkins, Baltimore), vol. 1, pp. 667-678.

15. Sachs RA, Daniel DM, Stone ML, et al. Patellofemoral problems after anterior cruciate ligament reconstruction. Am J Sports Med (1989);17:760-765

16. Kleipool AE, van Loon T, Marti RK. Pain after use of the central third of the patellar tendon for cruciate ligament reconstruction. Acta Orthop Scand (1994);65:62-66

17. Muellner T, Alacamlioglu Y, Nikolic A, Schabus R. No benefit of bracing on the early outcome after anterior cruciate ligament reconstruction. Knee Surg, Sports Traumatol, Arthroscopy (in press);


LPF ANGLE in deg (mean ± Std)






p1 =

Group A

9.3 ± 0.4

9.8 ± 0.5


Group B

9.8 ± 0.3

10.2 ± 0.3


p2 =





p1  p values obtained for the comparison of preoperative and postoperative values

p2 p values obtained for the comparison of group A and group B values preoperatively and postoperatively.


MERCHANT´S ANGLE in deg (mean ± Std)





p1 =

Group A

-1.1 ± 1.0

-2.8 ± 0.8


Group B

-1.3 ± 0.8

-6.0 ± 0.6


p2 =





p1  p values obtained for the comparison of preoperative and postoperative values

p2 p values obtained for the comparison of group A and group B values preoperatively and postoperatively







p1 =

Group A

1.13 ± 0.07

1.04 ± 0.12


Group B

1.16 ± 0.18

1.08 ± 0.15


p2 =





p1  p values obtained for the comparison of preoperative and postoperative values

p2 p values obtained for the comparison of group A and group B values preoperatively and postoperatively




Table 1: No statistically significant difference was found for the lateral patellofemoral (LPF) angle between groups A and B pre- and postoperatively.

Table 2: Although the pre- and postoperative differences in group A were minimal, they were statistically significant. On the other hand in group B the differences were distinct. Postoperatively a significant difference was found between the two groups, which was not present preoperatively

Table 3: The patella height differed significantly postoperatively compared to the preoperative values. Between the groups no significant difference was found.

Figure 1: The lateral patellofemoral angle (a) is determined by the junction of a line across the femoral condyles and another line drawn across the lateral patellar facet. The congruence angle (b) is determined by bisecting the sulcus angle, projecting a second line from the apex of sulcus to the lowest point of the patellar ridge; the angle is formed between this line and the bisecting line

Figure 2: For the calculation of the Insall Salvati Ratio the length of the patella is measured from the upper to the lower pole and the patellar tendon length is measured from the lower pole of the patella to a small depression in the tibia.


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