Patella ORIF — Tension Band and Screw Fixation

Surgical Indications

Absolute Indications

• Articular step-off greater than 2 mm or fracture gap greater than 3 mm on radiographs or CT
• Loss of active knee extension (inability to perform straight-leg raise)
• Open patellar fracture requiring debridement and stabilisation
• Displaced fracture with significant displacement of the extensor mechanism
• Associated ipsilateral injuries requiring surgical stabilisation (tibial plateau, distal femur)

Relative Indications

• Minimally displaced fracture (step-off less than 2 mm) with preserved active extension but patient preference for early mobilisation
• Athletes or high-demand patients where anatomic reduction may improve long-term function
• Comminuted fractures where partial patellectomy and tendon reattachment can restore a functional extensor mechanism

Contraindications

Absolute:

• Minimally displaced fracture with intact active extension and acceptable alignment for non-operative management
• Patient medically unfit for surgery
• Chronic non-union with established post-traumatic arthritis where salvage (patellectomy or arthroplasty) is more appropriate

Relative:

• Severe soft-tissue compromise requiring delayed definitive fixation
• Low-demand elderly patient with comorbidities where non-operative care in extension bracing is acceptable
• Vertical fracture patterns better suited to lag screw fixation alone

Evidence for Operative versus Non-Operative Treatment

Non-Operative Management

• Indicated for fractures with articular step-off less than 2 mm and an intact extensor mechanism
• Cylinder cast or hinged knee brace locked in extension for 4-6 weeks followed by progressive mobilisation
• Good to excellent results in 70-85% of appropriately selected minimally displaced fractures
• Risk of late displacement if patient compliance with extension bracing is poor

Operative Treatment Outcomes

• Anatomic reduction and stable fixation allows early mobilisation and reduces the risk of post-traumatic arthritis
• Modified anterior tension-band wiring achieves union rates greater than 90% in transverse fractures
• Cannulated screw tension-band constructs show lower rates of hardware prominence and re-operation compared with K-wire constructs in several series
• Partial patellectomy for comminuted poles restores extension with acceptable functional scores when at least 50% of patellar height is preserved

Key Evidence

Extensor Mechanism Anatomy

Patella

• Largest sesamoid bone in the body, embedded within the quadriceps tendon
• Articular surface is the thickest hyaline cartilage in the human body (up to 7 mm)
• Divided into medial and lateral facets by a central ridge; the medial facet has an odd facet that articulates only in deep flexion
• Blood supply enters via the anterior surface and the inferior pole (inferior geniculate artery) — the superior pole is relatively avascular

Quadriceps Tendon

• Convergence of rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius
• Inserts into the superior pole of the patella
• The medial and lateral patellar retinacula are expansions that reinforce the extensor mechanism on either side of the patella

Patellar Tendon

• Continuation of the quadriceps tendon distal to the patella
• Runs from the inferior pole of the patella to the tibial tubercle
• enveloped by the deep infrapatellar bursa and the prepatellar bursa anteriorly

Retropatellar Surface and Articular Reduction

• The retropatellar articular surface must be visualised directly during reduction
• A small arthrotomy or fracture-line visualisation allows the surgeon to palpate and inspect the articular surface
• Any residual step-off greater than 2 mm or gap greater than 3 mm must be corrected before final fixation

Vascular and Nerve Considerations

• The geniculate arteries form a rich anastomosis around the patella; the superior lateral and medial geniculates are at risk during the approach
• The infrapatellar branch of the saphenous nerve crosses the anterior knee and is frequently injured, leading to a numb patch lateral to the incision — counsel patients pre-operatively
• The common peroneal nerve is not at risk in the standard midline approach but must be protected if a lateral incision or extensive dissection is required

Biomechanics of the Modified Anterior Tension Band

• During knee flexion the quadriceps exerts a distractive force across a transverse patellar fracture
• The modified anterior tension-band construct places longitudinal implants (K-wires or screws) in the anterior half of the patella as a fulcrum
• The figure-of-eight wire lies anterior to this fulcrum; as the knee flexes, the wire tightens and converts the distractive force into articular compression
• This principle only works when the implants are placed anteriorly and the wire is tensioned correctly with the knee in extension before testing flexion

Positioning and Preparation

Patient position: Supine on a radiolucent table with a bump under the ipsilateral hip. The knee is flexed to 30-40 degrees over a radiolucent triangle or bump to relax the extensor mechanism. A tourniquet is applied to the thigh but is not inflated unless required for visualisation.

Anaesthesia: Regional (spinal or femoral-sciatic block) or general anaesthesia. A femoral nerve block or adductor canal block provides excellent post-operative analgesia.

Imaging: Image intensifier positioned for AP, lateral, and sunrise views. The C-arm should be able to rotate freely around the knee without repositioning the patient.

Consent: Discuss risks including hardware prominence requiring removal (20-50%), loss of reduction, non-union (less than 5%), infection (1-2%), extensor lag, post-traumatic arthritis, and the possible need for future salvage procedures.

Midline Anterior Approach — Step-by-Step

Step 1: Skin Incision and Exposure

Make a longitudinal midline incision centred over the patella, extending from the superior pole to the tibial tubercle. The incision can be curved slightly medially or laterally if there is an open wound or skin contusion on one side. Raise full-thickness skin flaps medially and laterally to expose the fracture and the extensor retinaculum. Identify and protect the infrapatellar branch of the saphenous nerve when encountered.

Step 2: Identify the Fracture and Extensor Mechanism

Expose the fracture line and the quadriceps tendon proximally and the patellar tendon distally. Palpate for gaps or discontinuities in the tendons. If a concomitant tendon rupture is suspected, extend the exposure proximally or distally to visualise the entire extensor mechanism.

Step 3: Evacuate Haematoma and Inspect the Articular Surface

Evacuate the fracture haematoma. If the fracture is transverse, the two main fragments can often be hinged open to visualise the retropatellar surface. If visualisation is inadequate, make a small medial or lateral arthrotomy to allow direct inspection and palpation of the articular surface. Remove loose osteochondral fragments that cannot be reconstructed.

Step 4: Reduce the Fracture

Use pointed reduction clamps or Weber clamps placed on the superior and inferior poles to achieve anatomic reduction. For transverse fractures, a pointed clamp placed across the fracture in the coronal plane often provides excellent control. Confirm reduction by direct palpation of the articular surface and with fluoroscopy.

Step 5: Provisional Fixation

Once reduced, place two parallel 1.6 mm or 2.0 mm K-wires longitudinally from superior to inferior pole, positioned in the anterior half of the patella. The wires should be parallel in both planes and spaced approximately one-third of the patellar width apart. Confirm position with fluoroscopy.

Step 6: Tension-Band Wiring

Pass a 18-gauge stainless-steel wire in a figure-of-eight pattern around the K-wires. The wire should pass through the quadriceps tendon proximally and the patellar tendon distally, or through drill holes in the poles if the tendon attachments are tenuous. Tighten the wire with the knee in extension, then gently flex the knee to 90 degrees while observing the fracture site. The wire should tighten and compress the articular surface rather than allow gapping.

Step 7: Cannulated Screw Tension-Band Alternative

For patients with thin soft-tissue envelopes or high functional demand, use 4.0 mm or 4.5 mm cannulated screws instead of K-wires. Drill over the provisional K-wires with a cannulated drill, measure, and insert partially threaded cannulated screws. Pass the tension-band wire through the screw heads or around the screws in a figure-of-eight. This construct is lower profile and has a lower re-operation rate for hardware removal.

Step 8: Partial Patellectomy for Comminution

When the inferior (or superior) pole is severely comminuted and cannot be reconstructed, excise the comminuted fragments. Reattach the patellar tendon (or quadriceps tendon) to the remaining patella with heavy non-absorbable transosseous sutures passed through drill holes or with suture anchors. Ensure at least 50% of the original patellar height remains to preserve the extensor lever arm.

Step 9: Final Imaging and Closure

Obtain AP, lateral, and sunrise fluoroscopic views. Confirm anatomic articular reduction, appropriate implant position, and no gapping with knee flexion. Irrigate the wound, achieve haemostasis, and close the retinaculum with absorbable suture. Close skin in layers. Apply a sterile dressing and a hinged knee brace locked in extension.

Post-operative Protocol

Immediate Post-operative (Day 0-14)

• Weight-bearing: Touch weight-bearing or partial weight-bearing in a hinged knee brace locked in extension for the first 2 weeks
• Brace: Locked in full extension at all times except for hygiene and physiotherapy
• Quadriceps activation: Isometric quadriceps setting exercises and straight-leg raises begin on day 1
• Analgesia: Multimodal including regional block, paracetamol, NSAIDs, and short course of opioids
• Wound care: Keep dressing clean and dry; review at 10-14 days for wound check and suture removal

Early Rehabilitation (2-6 weeks)

• Continue brace locked in extension for weight-bearing activities
• Begin gentle passive knee flexion to 30-40 degrees under physiotherapist supervision once wound is healed
• Continue active quadriceps exercises and straight-leg raises
• Progress to full weight-bearing in the brace as tolerated

Intermediate Phase (6-12 weeks)

• Radiographic review at 6 weeks: If bridging callus is present, unlock the brace for active-assisted range-of-motion exercises
• Advance flexion gradually to 90 degrees by 8-10 weeks
• Begin stationary cycling and closed-chain strengthening
• Wean from brace once quadriceps control is adequate and patient can perform straight-leg raise without lag

Late Phase (3-6 months)

• Full active and passive range of motion expected by 3 months
• Progressive resistance and proprioceptive training
• Return to sport or heavy labour at 4-6 months when strength is at least 80% of contralateral side and radiographic union is confirmed

Special Considerations

• Partial patellectomy patients: Longer period of protected weight-bearing (8-12 weeks) because the tendon-to-bone healing interface is weaker than bone-to-bone fixation
• Diabetic or immunocompromised patients: Slower progression, extended bracing, and closer wound surveillance
• Bilateral injuries: Staggered rehabilitation to allow one leg to support the other during recovery