coaxial stich test in total hip arthroplasty
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Coaxial Stitch Test in Total Hip Arthroplasty
The co-axial stitch (also called the co-axial suture technique) is an intraoperative limb length measurement and soft tissue balancing tool used during THA. It was developed to overcome the inconsistencies of conventional intraoperative tests and to give surgeons a reliable, reproducible reference for restoring limb length equality and optimizing hip stability - all without expensive equipment.
Concept and Rationale
Most conventional intraoperative limb length measurement techniques (iliac pin methods, calipers, etc.) use two reference points - one pelvic and one femoral - but fail to standardize the flexion position of the limb when measurements are taken. Even small changes in hip flexion during measurement can significantly alter readings, making results unreliable.
The co-axial stitch solves this by using two axes rather than two points. When the pelvic axis and the femoral axis are aligned co-axially (i.e., brought into the same line), the limb is always in the same standardized position each time a measurement is taken. This removes position-dependent variability.
Technique - Step by Step
Setup (Before Dislocation)
- Limb positioning: The hip is placed at 45° of flexion and the knee at 90° of flexion.
- Axis marking: A sterile marking pen and a long straight ruler are used to draw a continuous axis line connecting:
- A fixed skin anchor point proximal to the hip incision (along the line of the greater trochanter)
- Across the greater trochanter (GT)
- Down the femoral shaft
- Suture placement: A suture (the "co-axial stitch") is placed and anchored into the skin at the proximal fixed reference point, with a straight hemostat attached to its distal end.
- Reference mark: Using electrocautery, a mark is burned onto the greater trochanter at the point where the distal end of the hemostat aligns when the axes are co-axial. This mark is the baseline limb length reference.
Intraoperative Use
After hip dislocation and component implantation/trialing:
- The hip is reduced and the limb is repositioned to exactly the same 45°/90° position.
- The axes are re-aligned co-axially by the surgeon (pelvic and femoral axes brought back into line).
- The position of the suture/hemostat relative to the electrocautery mark on the GT is then read:
- Mark matches = limb length restored
- Hemostat distal to mark = lengthening has occurred
- Hemostat proximal to mark = shortening has occurred
Integration with 3D Functional Balancing
The co-axial stitch is used alongside the CAV (Combined Anteversion) wedge as part of a "3D functional balancing" approach to THA. The combined workflow is:
- After inserting the acetabular cup, trial reduction is done with a zero-offset modular head.
- The co-axial stitch reading is taken - this typically shows lengthening due to a conservative initial neck cut.
- Calcar milling / further neck resection is performed to match the pre-dislocation GT mark exactly.
- Once length is matched, progressively higher offset modular heads are trialed.
- The highest offset head that does not cause lengthening on the co-axial stitch reading is selected as the correct offset.
This ensures maximum achievable offset (for stability and soft tissue tension) is used without sacrificing limb length equality.
Use in Femoral Neck Fracture / Hemiarthroplasty
The co-axial stitch has also been applied to hip replacement for femoral neck fractures (NOF). In this setting, the technique is performed before head removal:
- With the fracture fragments temporarily fixed by screws (Johanssen screws), the hip is reduced.
- The co-axial stitch marks the GT position as a pre-arthroplasty reference.
- After THR/hemiarthroplasty, the same mark is used to confirm restoration of native limb length.
This is particularly useful because native anatomy has not yet been altered by the surgery, providing a true baseline.
Accuracy and Clinical Results
| Outcome | Finding |
|---|---|
| Limb length equality | High success rate vs. conventional methods |
| Post-operative perceived limb length discrepancy (POPLL) | Co-axial stitch predicts POPLL correctly in ~75% (3 of 4 patients) |
| Dislocation rate | Very low when combined with 3D functional balancing |
| Static anatomical parameters (CuO, CoL) | Poor correlation to POPLL - inferior to co-axial stitch method |
Importantly, static radiographic parameters (composite limb offset, composite limb length) correlate poorly with patients' postoperative perception of limb lengthening. The co-axial stitch, which is a functional/dynamic intraoperative test, performs better.
Advantages Over Conventional Methods
- No additional skin incision or iliac pin required
- No costly navigation or imaging equipment
- Standardizes limb position, eliminating flexion-dependent measurement error
- Simple, quick, and reproducible
- Can be combined with any surgical approach
- Applicable to both elective THA and arthroplasty for fracture
Limitations
- Skin is not a rigid reference point - the proximal anchor can shift, though firm anchoring minimizes this variability
- May be less reliable in cases of old NOF fractures with significant neck resorption or severely comminuted fractures
- The technique is still operator-dependent and requires familiarity
- Prediction of POPLL is good but not perfect (~75%)
Summary
The co-axial stitch is a practical, low-cost intraoperative technique that standardizes limb positioning during THA by aligning two axes (pelvic and femoral) co-axially. It provides a reproducible baseline reference mark on the greater trochanter before hip dislocation. After trialing components, the same standardized position is recreated and the GT mark is checked to confirm accurate limb length restoration. When combined with systematic offset optimization (using progressively higher offset heads), it forms the basis of a 3D functional balancing strategy that simultaneously addresses both instability and limb length discrepancy - two of the most common causes of patient dissatisfaction after THA.
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