Fitmore Versus CLS Stem in Total Hip Arthroplasty. Bilateral One-stage Operations

Main question: Will use of a stem design that allows anatomical reconstruction of the hip joint improve the outcome in terms of hip function and patient satisfaction without causing any adverse effects?

Background: Total hip arthroplasty with use of the most well documented implants is a safe and cost-effective procedure. In the Swedish Hip Arthroplasty register the CLS stem has a 16 years implant survival of 97, 5 %. It is a classic design which requires resection of most of the neck. The stem also intrudes into the greater trochanter which in patients with certain types of proximal hip anatomy makes proper introduction of the stem difficult. Finally it has a standard stem length which will jeopardise future stem removal should there occur any late infection or instability problems.

Short uncemented stems have been introduced to enable a more anatomic reconstruction of the hip joint and to cause less invasion of the femoral canal to facilitate future revision should it be necessary. A more conservative resection of neck could also be of value to improve the clinical outcome by improved hip function and patient satisfaction.

Purpose of the present study and design: In a prospective study the clinical outcome, stem fixation and bone remodelling around a short stem (Fitmore) will be studied. The main focus will be to evaluate patient reported outcomes especially concerning function, over all satisfaction, pain and activity. All patients will receive the same cup (Trilogy). This cup is chosen because it has a very thorough documentation in prospective RSA studies and in the Swedish hip arthroplasty register. All cups will be supplied with insert made of high molecular polyethylene (Longevity).

Number of hips in the study: 44 consecutive cases

Methods: EQ-5D including VAS-scale to evaluate pain and over all satisfaction, (specific questionnaire concerning side preference), Harris Hip Score, DXA, radiostereometry and gait analysis.

1. Clinical parameters: EQ-5D form (including VAS for pain and satisfaction) is filled in by the patients. Harris Hip Score is filled in by the examiner. SF-36 and activity scale (UCLA) is filled in by the patient. Patients also fill in a study specific form including questions about hip preferred and a pain drawing. Clinical parameters will be studied preoperative after 1, 2, 5, 7 and 10 years.
2. Conventional radiography: Examinations will be done preoperatively, postoperatively, after 1, 2, 5, 7 and 10 years.
3. Computed tomography: Preoperatively, after 1 and 7 years.
4. DXA measurements: Postoperatively, after 6 months, 1, 2, 5, 7 and 10 years.
5. Radiostereometry: Postoperatively, after 3 and 6 months, 1, 2, 5, 7 and 10 years.
6. Gait analysis: 1 and 2 years.

Focus of interest:

1. Patient reported outcomes and especially Oxford Hip Score will constitute our primary outcome parameter.
2. Conventional radiography (preop with metallic indicator to determine magnification) will include AP, True lateral and pelvic view.
3. Computed Tomography will be done for preoperative planning in 3D (a new software has been developed). Preoperative planning in 3D will be done for booth types of prostheses. A prerequisite is that we have 3D-models available for all implants used in the study. Preoperative planning will also be done in 2D.

The CT-examinations will be also used to measure the anteversion of the femur (preoperatively) and of the femoral component (1 year exam). The influence of this parameter on clinical results and fixation will be studied. CT at 7 years will be compared with previous examinations to study development of any osteolysis.

1. DXA - studies will be done to study bone remodelling in terms of changes of bone mineral density around the implant. Both the femoral- and the acetabular side will be studied.
2. Radiostereometry. The cup will be marked during surgery. Model based RSA for the cup Component will also be used. On the femoral side the femoral head centre will be used to measure stem migration. Tantalum markers will be inserted into the acetabular bone and proximal femur.

Femoral component migration will be measured as translations of the femoral head centre in three directions (medial/lateral, proximal/distal, anterior/posterior). Implant migration between the 6 months and 1 year follow up will constitute our second outcome parameter.

Comments: From previous studies of uncemented stems it has been found that these implants often subside up to 1-2 mm and some even more during 6 months (rarely up to 1 year) and may thereafter become stable and at least according to conventional radiography achieve osseous fixation.

Two years after the operation patients will also be studied using dynamic RSA during active abduction and flexion. The aim is to study any-lift off during these motions. A new radiostereometric laboratory has been installed in 2010 which has facilitated these types of examinations.

In addition the fixation of the cup and wear (femoral head penetration) will be measured.

1. Gait analysis will be performed one and two years after the operation. The patients will be studied walking and when rising from a chair. This analysis will focus on flexion/extension, motions of the hip and the knee and the ground reacting forces. The ab/adduction movements over the hip during walking will also be recorded.