Background:

Coronal malalignment occurs frequently in total knee arthroplasty (TKA) and reduces implant longevity and function. Designed to improve consistency and efficiency, patient- specific positioning guides (PSPG) generated from preoperative imaging studies represent a paradigm shift from manual instrumentation (MI) and intraoperative computer navigation.

Resurfacing arthroplasty of the hip enjoyed a resurgence of enthusiasm. A recent article has documented that the media played a significant role in its popularity, making claims that were not substantiated in scientific literature. Proponents of resurfacing arthroplasty state that it is bone conserving, provides greater stability, enhances range of motion, leads to a more normal gait, facilitates increased activity levels, decreases risk of dislocation, decreases the risk of leg length discrepancy and find that it is easier to insert in the face of deformity or retained hardware. The naysayers state that it is a more difficult operative procedure associated with a higher learning curve. They note that there are few patients who meet the selection criteria and there is an increased risk of fracture of the femoral neck. Finally, there is concern over metal ion toxicity and adverse tissue reaction. Furthermore, as we explore the literature, several studies have observed that resurfacing requires a bigger cup and results in a significantly higher volume of normal bone reamed from the acetabulum. Other studies note decreased range of motion with resurfacing compared with total hip arthroplasty (THA) secondary to an unfavourable head to neck ratio resulting in increased impingement. While resurfacing is purported to enhance functional outcomes, one randomized trial of 48 patients, 24 each resurfacing and large head THA, compared with 14 healthy control subjects found no difference in gait speed and postural balance evaluations, functional test, and clinical data at 3, 6 and 12 months post-operative. In another study comparing 337 resurfacings with 266 ceramic-on-ceramic THA, at 24 months there was no difference in Harris hip score, pain score or function score, but a statistically greater improved Harris hip range of motion score in THA. In a large meta-analysis study comparing 3269 hip resurfacings (3002 patients) with average follow-up of 3.9 years to 5907 cementless THA (5907 patients) with average follow-up of 8.4 years, the observed rate of femoral revision due to mechanical failure was 2.6% for resurfacing versus 1.3% for THA, yielding annualized rates of 0.67% and 0.15% respectively. An analysis of hip resurfacing data from national joint registries found that hip resurfacing demonstrates an overall increased failure rate compared with THA, except in males younger than 65 years old having a diagnosis of primary osteoarthritis and except with head diameters larger than 50 mm, which may be especially relevant as a contraindication for use of the procedure in female patients.

The goals of total knee arthroplasty (TKA) are to relieve pain, restore function, and provide a stable joint. In regard to types of implants, the workhorses are posterior cruciate retaining (CR), posterior stabilised (PS), and posterior stabilised constrained (PSC) designs. However, the continuum of constraint now ranges from standard cruciate retaining (CR-S) to CR lipped (CR-L), to anterior stabilised (CR-AS), to posterior stabilised, to a PS “plus” that fits with a PS femoral component but provides a small degree of varus-valgus constraint, to a PSC or constrained condylar type of device, to a rotating hinge. As the degree of deformity, bone loss, contracture, ligamentous instability and osteopenia increases, so does the demand for prosthetic constraint. When deformity is minimal and the posterior cruciate ligament (PCL) is intact and functional, a CR-S device is appropriate. For moderate deformity with deficiency or compromise of the PCL, a CR-AS or posterior stabilised device is warranted. In severe cases, with attenuation or absence of either of the collateral ligaments, a constrained condylar device, with options of stems, wedges and augments, is advisable. In salvage situations, when both collaterals are compromised, a rotating hinge should be utilised. Prerequisites for use of a CR-S device are an intact PCL, balanced medial and lateral collateral ligaments, and equal flexion and extension gaps. With a CR-L bearing, a slight posterior lip is incorporated into the sagittal profile of the component to provide a small amount of extra stability in the articulation. It is important for the surgeon to be aware of the design features of the implant system he or she is using. For example, in a system where the CR-S bearing has 3° of posterior slope and the CR-L bearing has no slope, the thickness of a CR-L bearing posteriorly is approximately 2 mm greater than the CR-S. A CR-L bearing is indicated for to provide stability where the flexion gap is just slightly looser than the extension gap and the PCL is intact. If the patient's knee is somewhat lax in flexion and stable in extension, a CR-L bearing may help to stabilize both the flexion and extension gaps yet still allow the knee to obtain full extension, whereas if a CR-S bearing in the next thicker size is used to stabilise the flexion gap, a flexion contracture may result. CR-AS bearings are required less frequently. They are indicated when the flexion and extension gaps are balanced, but the PCL is deficient, and the surgeon does not want to change to a PS design, which requires additional bony resection of intercondylar notch. The PCL is one of the strongest ligaments in the knee, and affords inherent stability to the TKA. In flexion, the PCL not only affords AP stability, but also imparts flexion gap stability, acting as a lateral stabilizer of the medial compartment and a medial stabiliser of the lateral compartment. The PCL has a crucial role with respect to femoral rollback, which imparts added efficiency to the extensor mechanism. PCL retention is a more biologically preserving operative intervention than PS-TKA.

Introduction

This study compares the incidence of post-operative complications (within 90 days) following primary total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA).