Effect Of Different Correction Angle Of Open Wedge High Tibial Osteotomy On Patellofemoral Pressure: A Biomechanical Study In Human Cadaveric Knees

Background: Opening wedge high tibial osteotomy (OWHTO) is aneffective treatment for unicompartmental varus osteoarthritis. Shifting theloading axis from the degenerated medial part of the joint to the lateralcompartment can decompress medial overload so as to reduce the pain anddelay the progression of osteoarthritis. Although after reviewing the literatureof the short-term and long-term follow-up results of HTO, the overalltreatment effect is good, the incidence of patella position changing such aspatella infra was about as high as89%. Previous studies only focus on thecomparation of patella position preoperative and postoperative, and neglectedthe different patella infra or the different patella height severity caused bydifferent correction angle. They never analysis the statistical relationshipbetween the correction angle and the patella infra or the patella height.Purpose: The objective of this study is to investigate the effects ofdifferent correction angle on patella position and patellofemoral jointpressures and patella kinematics in a human cadaver model.Study Type: Cadaveric study.Methods: Eight fresh frozen human cadaveric knee specimens (ageranges from26to45years) were cut10cm from the joint line. The knees weredissected of all skin and subcutaneous tissue. All knees had not been injured oroperated on previously. Biplanar radiographs were taken to exclude anyosseous pathology or trauma. The knee specimens were wrapped in watersoaked cloth, and stored at–70°C in plastic bags. The specimens were thawedover48h before testing. All testing was conducted under regulations outlinedby Hebei Medical University.An osteotomy of the proximal tibia wasperformed about3-4cm below the tibial joint line or2cm above the tibial tubercle and directed to superior tibiofibular joint, with the lateral bone cortexnot completely divided. Gradually opened the bone cut wide using flat chiselsand sequentially tapped plastic wedges into the gap to achieve the suitablecorrection angle The correction angle ranges from the physiological condition(incision closed) to15°in5°increments per time. A special external fixatorwith two pins proximal and two pins distal to the osteotomy incision wasmounted to stabilize the correction angle. Eight fresh cadaveric kneespecimens were positioned at the flexion angle of30°,60°and90°respectively in vitro, and were applied400N of tension forces through thequadriceps. During the experiment, the patellar height was measured by Catonindex, lateral patellar shift (LPS) was defined as the ratio of the distancesPP'/CC' and the pressure applied to lateral and medial patellofemoral cartilagewas measured with the Tekscan pressure sensors. In a lateral view, the Catonindex is the ratio of the distance from the lower edge of the articular surface ofthe patella to the anterosuperior angle of the tibia outline (AT) to the length ofthe articular surface of the patella (AP) at30°of flexion. In a standing skylineview, LPS is defined as the ratio of the distances PP'/CC'. CC' is defined as thedistance between the summits of the medial and lateral femoral condyles ofthe femur. PP' is defined as the distance between the summit of the lateralfemoral condyle and the point where a line from the lateral edge of the patellaperpendicular to the line that passes through the summits of the femoralcondyles crosses that line.Results:1At5°correction, the lateral patellofemoral pressure increased by1.9%in30°of flexion,4.6%in60°of flexion and3.3%in90°of flexion, andthe medial patellofemoral pressure increased by－20.0%in30°of flexion,4.3%in60°of flexion and－0.9%in90°of flexion. At10°correction, thelateral patellofemoral pressure increased by15.8%in30°of flexion,25.6%in60°of flexion and21.9%in90°of flexion, and the medial patellofemoralpressure increased by－10.2%in30°of flexion,13.8%in60°of flexion and20.2%in90°of flexion. At15°correction, the lateral patellofemoral pressure increased by39.9%in30°of flexion,22.6%in60°of flexion and4.8%in90°of flexion, and the medial patellofemoral pressure increased by23.4%in30°of flexion,40.5%in60°of flexion and4.6%in90°of flexion.2In30°of flexion, the lateral patellofemoral pressure increased by1.9%at5°correction,15.8%at10°correction and39.9%at15°correction,and the medial patellofemoral pressure increased by－19.7%at5°correction,－10.2%at10°correction and23.4%at15°correction. At60°of flexion, thelateral patellofemoral pressure increased by4.6%at5°correction,25.6%at10°correction and22.6%at15°correction, and the medial patellofemoralpressure increased by4.3%at5°correction,13.8%at10°correction and40.5%at15°correction. At90°of flexion, the lateral patellofemoral pressureincreased by3.3%at5°correction,21.9%at10°correction and4.8%at15°correction, and the medial patellofemoral pressure increased by－0.9%at5°correction,20.2%at10°correction and4.6%at15°correction.3the peak pressure of the lateral and medial patellofemoral cartilageincreased (P<0.05) with the correction angle increasing, because of the lateralshift of the patella, the lateral patellofemoral peak pressure was raised muchmore higher than that of the medial. The patella height was evaluated using thecaton index. The nomal caton idex in the study was0.85±0.04. The mean5°,10°and15°correction's caton index were0.79±0.06,0.72±0.08and0.66±0.05respectively. The LPS was evaluated using PP'/CC'. The preoperative LPS was9.51±0.25%. The mean5°,10°and15°correction's LPS were10.06±0.28,10.21±0.22and10.31±0.12%. Postoperative LPS was significantly differentfrom the nomal group (P<0.05).Conclusions: We conclude from these results that the OWHTO can leadthe patella to move downwards and outwards. With the correction angleincreases, the patella infra and the LPS infra increased, causing much higherpressure applying on the patellofemoral joint. The overpressure may lead tothe degenerative changes of the patellofemoral joint. Patella-femoral arthritiswill happen when the pressure exceeds the pressure limit. Our results showthat correction angle significantly affects patella position and the cartilage pressure of the patellofemoral joint. Specifically in walking state(in30°offlexion), the peak patellofemoral pressure rises by1.9%(P＞0.05) at5°correction,15.8%(P＜0.05) at10°correction and39.9%(P＜0.05) at15°correction. The data show that5°correction has no obvious effects on thepatellofemoral pressure. The implication of these data for clinical use is thatcorrection angle should be taken into consideration when this technique isdecided to be performed. Especially in large correction angle significantchanges in patellar height and tracking can be induced, we can choose thebiplane osteotomy or the dome-type osteomy.