The Role Of Medial And Lateral Soft Tissue Of Patella On The Stability Of Patella

Objective: Patella plays an important role in extensor mechanism. Thestability and normal trajectory of the patellar depends on the normalbone-structure of the knee and the balance of the medial and lateral soft tissueof patellar. Fully awareness of the mechanisms of medial and lateral softtissues of patellar, contribute to the understanding of the pathologicalmechanism of patellar instability, and to make the right diagnosis andreasonable treatment with the theory. The purpose of this study was to explorethe impact of the medial and lateral soft tissue structure of patella on thestability of the patella with the normal bony structure of the knee.Method: Totally8fresh-frozen cadaveric knees with the normal bonystructure were used in the study. Both the distal femur and proximal tibiaapproximate20cm from the joint line were reserved for each specimen, andthe skin of knee joint was resected. Then the specimen was placed onto thehomemade knee joint retention mechanism. The CT scan was performed onthe patellofemoral joint with the integrity of medial and lateral soft tissue, andthe scan images were saved (Group N). A longitudinal dissection was madealong the medial border of the patella so as to separate the medial retinaculumand capsule from the patella. An anchor was fixed at the midpoint of thelateral border of the patella, then, a weight of2Kg was hanging on the otherside of the anchor. The weight of2Kg imposed horizontal lateral vector on thepatella through the pulley on the homemade knee joint retention mechanism.The CT scan was performed on the patellofemoral joint with the medial softtissue was dissected, and the scan images were saved (Group M). Then thedissected medial soft tissue was sutured in-situ. A longitudinal dissectionwas made along the lateral border of the patella so as to separate the lateralretinaculum and capsule from the patella. An anchor was fixed at the midpoint of the medial border of the patella, then, a weight of2Kg was hanging on theother side of the anchor. The weight of2Kg imposed horizontal medial vectoron the patella through the pulley on the homemade knee joint retentionmechanism. The CT scan was performed on the patellofemoral joint with thelateral soft tissue was dissected, and the scan images were saved (Group L).Finally, the scanned images of these3groups was measured, includingcongruence angle (CA) and patellar tilt angle (PTA) and Lateral patellardisplacement (LPD). The SPSS16.0statistical software was separately usedfor finding the statistical significance of CA, PTA, LPD between Group N andGroup M, Group N and Group L, Group M and Group L.Results: The CT scan was performed on the patellofemoral joint with theintegrity of medial and lateral soft tissue, the measurements of CA (°), PTA (°),LPD (mm) were4±1.3,3±1.0,4.5±1.2respectively, all of them under thenormal range. The CT scan was performed on the patellofemoral joint with themedial soft tissue was dissected with a weight of2Kg imposed horizontallateral vector on the patella through the pulley on the homemade knee jointretention mechanism, the measurements of CA (°), PTA (°), LPD (mm) were39±2.8,16±1.4,23±1.6respectively. The measurements of CA, PTA, LPDwere increased significantly compared with Group N（P<0.05）. After thedissected medial medial soft tissue was sutured in-situ, the CT scan wasperformed on the patellofemoral joint with the lateral soft tissue was dissectedwith a weight of2Kg imposed horizontal medial vector on the patella throughthe pulley on the homemade knee joint retention mechanism, themeasurements of CA (°), PTA (°), LPD (mm) were50±2.7,27±2.6,14.5±1.9.The measurements of CA, PTA, LPD were increased significantly comparedwith Group N（P<0.05）. Then, the measurements of CA, PTA, LPD werecompared between Group M and Group L, there were statistically significantdifferences between2groups（P<0.05）.Conclusions:1. The stability and normal trajectory of the patellardepends on the balance of the medial and lateral soft tissue of patellar.2. Themain role of patellar medial soft tissue was to restrict the lateral displacement of the patella, so as to effectively prevent patellar dislocation.3. The main roleof patellar lateral soft tissue was to prevent excessive rotation of the patella, soas to effectively prevent patellar tilt and maintaining the normal trajectory ofpatella.