Tibiofemoral Alignment in Posterior Stabilized Total Knee Arthroplasty: Static Alignment Does Not Predict Dynamic Tibial Plateau Loading Emily J. Miller, Mark W. Pagnano, Kenton R. Kaufman Department of Orthopedic Surgery, Mayo Clinic Rochester, Motion Analysis Laboratory, 200 First Street SW, Charlton North L-110, Rochester, Minnesota 55905 Received 5 September 2013; accepted 15 April 2014 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.22644
ABSTRACT: For total knee arthroplasty (TKA), neutral mechanical alignment produces balanced static knee loading. Dynamically, knee loading is affected by more than limb static alignment. We compared static and dynamic knee loading following TKA. Fifteen TKA patients were evaluated pre-operatively and 2 months and 2 years post-operatively. Tibiofemoral angles and medial tibial plateau loading were calculated. Pre-operatively, static medial load was greater for varus than valgus knees. Post-operatively, no relationship existed between tibiofemoral angle and static medial plateau load. Pre-operatively and post-operatively, dynamic medial load was not dependent on tibiofemoral angle. While all patients achieved equal static plateau load distributions at 2 years, only 47% had dynamic medial load distributions of 50 10%. Static tibiofemoral alignment alone does not predict dynamic tibial loading. ß 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res Keywords: knee; alignment; medial plateau load; gait; knee replacement arthroplasty
A surgical goal in total knee arthroplasty (TKA) is to obtain neutral mechanical alignment within 3˚ as determined on static full-length radiographs of the hip–knee–ankle.1–6 This is considered necessary to achieve optimal function, produce balanced medial and lateral loading distributions, and prolong implant longevity.4,7,8 Under static loading, tibiofemoral alignment angle deviations of 3˚ greatly alter the distribution of pressure and load between the medial and lateral tibial plateaus.6 It was suggested that proper mechanical axis alignment produces balanced medial and lateral loading distributions that reduce polyethylene wear and adverse joint mechanics.6,9 However, other studies challenged the practice that neutral coronal plane tibiofemoral alignment improves implant longevity.10–13 These studies did not show a statistical difference in the number of revision surgeries between well aligned knees and mechanical alignment outliers (varus/valgus knees). It was suggested that accurate alignment allows for improved kinematics and improved outcomes in TKA patients.14 Knowledge of tibial plateau loading during gait after TKA may provide insight into why controversy exists over the long-term risk of failure between mechanically well-aligned knees and mechanical alignment outliers.1,9–13,15–17 We assessed dynamic tibial plateau loading following TKA. We hypothesized that a relationship exists between tibiofemoral angle and medial plateau load for static, but not for dynamic loading.
METHODS Patients undergoing TKA enrolled in a larger, short-term post-operative follow-up, prospective, randomized, controlled, blinded study comparing functional outcomes of two contem-
Conflicts of interest: None. Grant sponsor: Mayo Clinic. Correspondence to: Kenton R. Kaufman (T: þ1-507-284-2262; F: þ1-507-266-2227; E-mail: [email protected]) # 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.
porary surgical procedures (mini sub-vastus vs. mini-medial arthrotomy) were analyzed. This study was described to eligible candidates during an initial physician visit. Patients who met inclusion and exclusion criteria (Table 1), gave written informed consent, and agreed to return for a second long-term (2 years) post-operative assessment participated. Fifteen (Table 2) of the 41 patients enrolled in the short-term study participated in this long-term study. During surgery, the cruciate ligaments were carefully excised, and all knees were fitted with a cemented posterior stabilized TKA (Sigma PS; DePuy; Warsaw, IN). Specific attention was made to intra-operatively balance the medial and lateral ligaments with the aid of spacer-blocks available in 1 mm increments. After confirming that appropriate bony resection had been done, ligamentous asymmetry was typically addressed by release of the tight side until balance within 1 mm was achieved and confirmed with the appropriate spacer-block. In no case was a complete release of either the medial or lateral collateral ligaments required. When residual medial tightness was present, a graduated sub-periosteal release was done to obtain symmetry within 1 mm, and when lateral sided tightness was present a pie-crust or multiple puncture release of the iliotibial band was done. Flexion and extension gaps were assessed with the use of spacer blocks, and all the patients were judged by an experienced, senior surgeon (MWP) to have excellent post-operative ligamentous balance. All patients returned at 2 months and at 2 years for clinical evaluation. All knees were judged clinically to be stable in varus–valgus in extension and at 90˚ flexion and in the AP direction at 90˚ of flexion. Specifically, every knee underwent l physical examination by an experienced clinician in which the degree of ligamentous laxity was estimated in groups of (a) 10 mm of laxity in both varus–valgus and anterior translation. All knees were judged to have
ABSTRACT: For total knee arthroplasty (TKA), neutral mechanical alignment produces balanced static knee loading. Dynamically, knee loading is affected by more than limb static alignment. We compared static and dynamic knee loading following TKA. Fifteen TKA patients were evaluated pre-operatively and 2 months and 2 years post-operatively. Tibiofemoral angles and medial tibial plateau loading were calculated. Pre-operatively, static medial load was greater for varus than valgus knees. Post-operatively, no relationship existed between tibiofemoral angle and static medial plateau load. Pre-operatively and post-operatively, dynamic medial load was not dependent on tibiofemoral angle. While all patients achieved equal static plateau load distributions at 2 years, only 47% had dynamic medial load distributions of 50 10%. Static tibiofemoral alignment alone does not predict dynamic tibial loading. ß 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res Keywords: knee; alignment; medial plateau load; gait; knee replacement arthroplasty
A surgical goal in total knee arthroplasty (TKA) is to obtain neutral mechanical alignment within 3˚ as determined on static full-length radiographs of the hip–knee–ankle.1–6 This is considered necessary to achieve optimal function, produce balanced medial and lateral loading distributions, and prolong implant longevity.4,7,8 Under static loading, tibiofemoral alignment angle deviations of 3˚ greatly alter the distribution of pressure and load between the medial and lateral tibial plateaus.6 It was suggested that proper mechanical axis alignment produces balanced medial and lateral loading distributions that reduce polyethylene wear and adverse joint mechanics.6,9 However, other studies challenged the practice that neutral coronal plane tibiofemoral alignment improves implant longevity.10–13 These studies did not show a statistical difference in the number of revision surgeries between well aligned knees and mechanical alignment outliers (varus/valgus knees). It was suggested that accurate alignment allows for improved kinematics and improved outcomes in TKA patients.14 Knowledge of tibial plateau loading during gait after TKA may provide insight into why controversy exists over the long-term risk of failure between mechanically well-aligned knees and mechanical alignment outliers.1,9–13,15–17 We assessed dynamic tibial plateau loading following TKA. We hypothesized that a relationship exists between tibiofemoral angle and medial plateau load for static, but not for dynamic loading.
METHODS Patients undergoing TKA enrolled in a larger, short-term post-operative follow-up, prospective, randomized, controlled, blinded study comparing functional outcomes of two contem-
Conflicts of interest: None. Grant sponsor: Mayo Clinic. Correspondence to: Kenton R. Kaufman (T: þ1-507-284-2262; F: þ1-507-266-2227; E-mail: [email protected]) # 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.
porary surgical procedures (mini sub-vastus vs. mini-medial arthrotomy) were analyzed. This study was described to eligible candidates during an initial physician visit. Patients who met inclusion and exclusion criteria (Table 1), gave written informed consent, and agreed to return for a second long-term (2 years) post-operative assessment participated. Fifteen (Table 2) of the 41 patients enrolled in the short-term study participated in this long-term study. During surgery, the cruciate ligaments were carefully excised, and all knees were fitted with a cemented posterior stabilized TKA (Sigma PS; DePuy; Warsaw, IN). Specific attention was made to intra-operatively balance the medial and lateral ligaments with the aid of spacer-blocks available in 1 mm increments. After confirming that appropriate bony resection had been done, ligamentous asymmetry was typically addressed by release of the tight side until balance within 1 mm was achieved and confirmed with the appropriate spacer-block. In no case was a complete release of either the medial or lateral collateral ligaments required. When residual medial tightness was present, a graduated sub-periosteal release was done to obtain symmetry within 1 mm, and when lateral sided tightness was present a pie-crust or multiple puncture release of the iliotibial band was done. Flexion and extension gaps were assessed with the use of spacer blocks, and all the patients were judged by an experienced, senior surgeon (MWP) to have excellent post-operative ligamentous balance. All patients returned at 2 months and at 2 years for clinical evaluation. All knees were judged clinically to be stable in varus–valgus in extension and at 90˚ flexion and in the AP direction at 90˚ of flexion. Specifically, every knee underwent l physical examination by an experienced clinician in which the degree of ligamentous laxity was estimated in groups of (a) 10 mm of laxity in both varus–valgus and anterior translation. All knees were judged to have
