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Letters to the Editor |
Los Angeles, California
Dear Editor:
I read with great interest the article by Järvelä et al. entitled "The Incidence of Patellofemoral Osteoarthritis and Associated Findings 7 Years after Anterior Cruciate Ligament Reconstruction with a Bone-Patellar Tendon-Bone Autograft" (January/February 2001, pages 18 to 24). Patellofemoral dysfunction after ACL reconstruction remains a significant problem, which this article has confirmed by demonstrating that 47% of patients had mild-to-moderate degenerative changes in the patellofemoral joint. The authors suggest that shortening of the patellar tendon correlates with the severity of patellofemoral joint osteoarthritis and admit that further studies are needed to verify the finding related to shortening of the patellar tendon and to clarify the main determinants of shortening.
Patella infera has been well documented after ACL reconstruction, both clinically and experimentally in animal models.2,3 Of great interest is determining the mechanism by which patellar tendon shortening leads to the osteoarthritis and also designing prevention strategies to avoid patellar tendon shortening. We have previously demonstrated in a biomechanical study that patellar tendon adhesion to the anterior tibia, without intrinsic tendon shortening, displaced the patella toward the tibial tuberosity, effectively creating apparent patella infera.1 The simulated patellar tendon adhesion directed the patellar tendon force more posterior, thus increasing the patellofemoral joint reaction force. This is similar to a more posterior-directed patellar tendon force observed in the setting of PCL insufficiency, which has also been associated with patellofemoral joint osteoarthritis and has been referred to as the reverse Maquet effect.4 Other effects of patellar tendon adhesion on knee mechanics demonstrated in our study were decreased patellar mobility and decreased effective moment arm of the extensor mechanism. These results alter patellofemoral mechanics and support a stress-based hypothesis for the development of patellofemoral osteoarthritis.
It would be interesting to know if the patients in the current study had clinically decreased patellar mobility and if the authors believe that patellar tendon scarring to the anterior tibia with the associated pathomechanics led to the observed osteoarthritis in their patients.
REFERENCES
Tampere, Finland
We thank Dr. Ahmad for his valuable comments concerning our article and we share his views.
It is true that the shortening of the patellar tendon correlates with the severity of the patellofemoral osteoarthritis. However, one must keep in mind that this is not the only factor that correlates to the patellofemoral osteoarthritis. We also studied whether the placement of the graft has some correlation to the patellofemoral osteoarthritis seen among our patients. We said in the "Discussion" section of our article that the patients with patellofemoral osteoarthritis tended to have more anterior placement of the femoral tunnel and more posterior placement of the tibial tunnel than did the patients without patellofemoral osteoarthritis, although, in this respect, no statistically significant correlation was found. However, now we have found, in another study, that the graft placement also correlates to the patellofemoral osteoarthritis: the patients with incorrect placement of the graft do have more patellofemoral osteoarthritis than the patients with good graft placement.1
We agree with Dr. Ahmad’s comments that patella infera after ACL reconstruction with a bone-patellar tendon-bone autograft has been well documented. However, the clinical significance of this change is not well documented. That is why we wanted to analyze the relationship of the shortening of the patellar tendon and the clinical outcome of the patients in our study.
Dr. Ahmad states that, in their biomechanical study, patellar tendon adhesion to the anterior tibia displaced the patella toward the tibial tuberosity, creating apparent patella infera and decreasing patellar mobility. Unfortunately, we did not record patellar mobility or patellar tendon scarring to the anterior tibia in our patients; we only recorded whether the patella was stable or not (subluxation). However, one additional point needs consideration. The closure of the patellar tendon defect with sutures after harvesting a middle-third of the tendon may have had some influence on the shortening and scarring of the residual patellar tendon in all of our patients. This could be an additional reason for the dysfunction of the extensor mechanism of the knee and thus degenerative changes of the patellofemoral joint.
REFERENCES
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