Abstract
Introduction:
Repair of the arthrotomy is a performed at the end of every total knee arthroplasty (TKA). After the arthrotomy is performed, most surgeons attempt to close the arthrotomy with the medial and lateral edges anatomically approximated. If no landmarks are made prior to performing the arthrotomy however, there is a risk that anatomic approximation may not be obtained. This study looked into the biomechanical changes in stiffness of the knee before and after a medial parapatellar approach repaired with an anatomic, and shifted capsular repair with the medial side of the arthrotomy shifted up or down when repaired to determine if capsular closure may have an effect on the stiffness of the joint.
Methods:
Fourteen cadaveric TKA specimens were retrieved through the Medical Education and Research Institute (Memphis TN). For each specimen tested, the skin and muscle tissue was removed, and the femur and tibia were cut transversely 180 mm from the joint center. Specimens were fixed in extension in a custom knee testing platform (Little Rock AR) and subjected to a 10 Nm varus and valgus torque and a 1.5 Nm internal and external rotational torque. The angle at which these moments occurred was recorded, and each test was repeated for 0, 30, 60, and 90 degrees of flexion. After tests were performed on retrieved TKA specimens, a fellowship trained orthopedic surgeon vented the knee capsule by making an incision with a number 10 scalpel blade in a horizontal nature to provide a landmark for anatomic reapproximation. Tests were repeated as before, after which the surgeon performed a standard arthrotomy and repaired it using #0 suture and a neutral alignment. Sutures were cut and the repair was repeated using upward 5 mm shift and downward 5 mm shift of the medial side of the arthrotomy during the repair. All tests were repeated after each repair technique. Any increase or decrease in laxity after capsule repair was referenced to the TKA laxity tested prior to an arthrotomy being performed.
Results:
Simply venting the capsule did increase laxity of the TKA in midflexion to varus torque by 3 degrees under the same torque. Otherwise, when the medial limb of the arthrotomy was shifted up during closure by 5 mm, the knee joint tended to be stiffer in flexion compared to the neutral repair measurements under varus torque, while it was closer to the measurements of the neutral or anatomic closure when the medial limb was shifted down during closure. These changes seemed to be seen in flexion more than full extension.
Discussion and Conclusion:
Small changes were measured in the stiffness of the joint after venting the capsule and under different degrees of non-anatomic closure. The results stress the fact that the capsule can be measurably tightened during arthrotomy repair and may impact post-operative rehabilitation or range of motion.
