The association between obesity and sleep apnea syndrome (SAS) is well known, as is the fact that TJR patients are often obese. Based on review of 5819 primary TJR patients at our institution, 53% of patients presenting for TJR were obese (mean BMI 31), and of those obese patients 61.3% were female. The potential impact of SAS, diagnosed and undiagnosed, on TJR outcomes has not been well described. In the literature it has been suggested that such patients may be at increased risk of prolonged hospital length of stay (LOS), increased risk of postoperative MI, and risk of postoperative respiratory compromise requiring unplanned transfer to a special care unit (SCU). At our institution, unless deemed required for preoperatively identified co-morbidities, all TJR patients are managed acutely on an orthopaedic ward with no formal step down unit available for enhanced monitoring, even when receiving PCA or epidural for postoperative pain control.

We undertook a prospective non-randomised survey of 1927 primary TJR patients over a fifteen-month period to screen for a preoperative diagnosis of SAS, or symptoms suggestive of SAS using the self-report Epworth Sleep Apnea Questionnaire. In addition, we evaluated impact of SAS on LOS, risk of postoperative MI, risk of postoperative respiratory compromise and unplanned transfer to SCU.

Of our sample, 88/1927 patients (4.6%) had a confirmed preoperative diagnosis of SAS. An additional 74/1927 patients (3.8%) had 3/3 symptoms suggestive of undiagnosed SAS. SAS patients were younger; mean sixty-six years, p=0.005, and predominantly male; 58%, p< 0.0001, as compared to non-SAS patients comprised of 60% females and mean age sixty-nine years. Mean BMI was higher in the SAS group; 32.3 versus 30, p< 0.0001. There was no correlation between SAS and risk of postoperative MI, LOS (mean 5.2 days, both groups), nor unplanned SCU admission.

Despite concerns expressed in the literature, we found that SAS, both diagnosed and suspected, was not associated with prolonged LOS, increased risk of postoperative MI, postoperative respiratory compromise, or unplanned postoperative transfer to a SCU.

Introduction: During total hip arthroplasty various femoral stem offsets are available and the femoral stem can be placed in either varus or valgus. The overall effect of this is to increase or decrease the functional offset at the hip joint. Many authors have investigated the effects of the functional offset upon the reconstructed hip joint. To our knowledge no studies have concentrated on the effects, if any, upon the loading and function of the knee joint. The aim of this study was to investigate the effects, if any, of reducing functional offset at the knee.

Materials and methods: To study the effects of alterations in functional offset during hip arthroplasty, a biomechanical computer model was constructed. Normal lower limb anthropometric measurements available in the literature were used within this program. The model thus constructed calculated the effect of different functional offsets upon moments about the knee in stationary standing on one leg. The model also allowed for different varus/valgus placement of the stem.

Results: Reducing prosthetic neck length reduces the moment arm created by the ground reaction force about the knee axis. Placing the stem in valgus reduces the moment arm. This reduction depends upon the length of the neck.

Discussion: In the one legged stance, the line of weight is offset in the coronal plane from the AP axis of the knee joint producing an adducting moment about the knee, balanced by tension in the lateral collateral ligament of the knee and the iliotibial tract. Any reduction in this moment arm would alter the loading of the knee, altering the value of the force on the lateral compartment of the knee. Indeed, it is possible to develop a situation where the knee moment arm creates an abducting moment about the knee, increasing the loading of the lateral compartment of the knee. This may lead to valgus malalignment of the knee.