Medial and lateral gap laxity differential in computer-assisted kinematic total knee arthroplasty

Abstract

AimsThe results of kinematic total knee arthroplasty (KTKA) have been reported in terms of limb and component alignment parameters but not in terms of gap laxities and differentials. In kinematic alignment (KA), balance should reflect the asymmetrical balance of the normal knee, not the classic rectangular flexion and extension gaps sought with gap-balanced mechanical axis total knee arthroplasty (MATKA). This paper aims to address the following questions: 1) what factors determine coronal joint congruence as measured on standing radiographs?; 2) is flexion gap asymmetry produced with KA?; 3) does lateral flexion gap laxity affect outcomes?; 4) is lateral flexion gap laxity associated with lateral extension gap laxity?; and 5) can consistent ligament balance be produced without releases?Patients and MethodsA total of 192 KTKAs completed by a single surgeon using a computer-assisted technique were followed for a mean of 3.5 years (2 to 5). There were 116 male patients (60%) and 76 female patients (40%) with a mean age of 65 years (48 to 88). Outcome measures included intraoperative gap laxity measurements and component positions, as well as joint angles from postoperative three-foot standing radiographs. Patient-reported outcome measures (PROMs) were analyzed in terms of alignment and balance: EuroQol (EQ)-5D visual analogue scale (VAS), Knee Injury and Osteoarthritis Outcome Score (KOOS), KOOS Joint Replacement (JR), and Oxford Knee Score (OKS).ResultsPostoperative limb alignment did not affect outcomes. The standing hip-knee-ankle (HKA) angle was the sole positive predictor of the joint line convergence angle (JLCA) (p < 0.001). Increasing lateral flexion gap laxity was consistently associated with better outcomes. Lateral flexion gap laxity did not correlate with HKA angle, the JLCA, or lateral extension gap laxity. Minor releases were required in one third of cases.ConclusionThe standing HKA angle is the primary determinant of the JLCA in KTKA. A rectangular flexion gap is produced in only 11% of cases. Lateral flexion gap laxity is consistently associated with better outcomes and does not affect balance in extension. Minor releases are sometimes required as well, particularly in limbs with larger preoperative deformities. Cite this article: Bone Joint J 2019;101-B:331–339.

Short- to mid-term outcomes of computer navigation assisted total knee arthroplasty using adjusted mechanical alignment compared to mechanical alignment

“…In the aMA group, the lateral gap laxity was wider than the medial gap and a wider exion gap laxity was produced, which is consistent with the ndings reported by Yoo et al in normal knee joint [38]. In addition, the lateral exion gap was signi cantly wider in the aMA group with a mean of 0.71 mm more laxity than the MA group, which matches the results of McEwen et al, who revealed a wider lateral exion gap laxity (>2 mm) was associated with better clinical and functional outcomes [39].…”

Intraoperative Midflexion Medial Laxity Affects Patient Expectations Following Total Knee Arthroplasty

“…Normal gap laxities have been reported using various methods. The exion gap has been reported to be wider than the extension gap [9][10][11], and the lateral exion gap tends to be greater than the medial exion gap in normal knees [5,7,10,11,[12][13][14]. It is not known how much intraoperative ligament imbalance is permitted during TKA.…”

An alternative technique of restricted kinematic alignment of the femur and gap balanced alignment of the tibia using computer aided navigation

“… 8 , 9 The authors feel it is key to restore the isometric medial compartment balance/gap in extension and flexion, but some laxity (increased gap) can be tolerated in the lateral compartment, for which there is evidence of improved patient outcomes. 10 …”