29 Peroneal Groove Deepening for Peroneal Subluxation Abstract The peroneal tendons run within a concave groove in the retrofibular region as they cross behind the ankle, and are held in place by the superior peroneal retinaculum (SPR). Forceful firing of the peroneal tendons during an eversion injury can result in stretching, tearing, or avulsion of the SPR and dislocation or subluxation of the peroneal tendons out of the groove. This can be predisposed to by having a shallow or even convex retrofibular groove, but can occur even in patients with a relatively normal groove depth. There are two variations of peroneal subluxation, one where one or both of the tendons sublux or dislocate completely out of the groove and a variation where the peroneus longus and brevis sublux within the sheath—reversing their anatomic positions causing dysmotility and pain. This condition is addressed by a deepening procedure of the retrofibular peroneal groove as outlined in this chapter. Keywords: retrofibular groove, groove deepening, fibular osteotomy, peroneal tendons, peroneal subluxation, peroneal dislocation • The primary indication is subluxation or dislocation of the peroneal tendons associated with a convex groove on the posterior fibula. • A secondary indication is the presence of any tear or pathology requiring reconstruction of the peroneal tendons passing through the retromalleolar space. Substantial pressure reduction on the peroneal tendons occurs with groove deepening even in the presence of normal fibular morphology; groove deepening has been advocated as a biomechanical adjunct to reconstructive procedures.1 • The normal retromalleolar groove is concave. In the presence of a convex groove, subluxation of one or both tendons is more likely to occur around the posterolateral margin of the fibula. • Subluxation may occur as a result of an acute injury or from chronic attrition of the insertion of the superior peroneal retinaculum (SPR) on the posterior margin of the distal fibula. • Typically, the periosteum of the posterolateral fibula will also be elevated, resulting in a periosteal pouch in continuity with the peroneal sheath. Alternatively, a small avulsion of the fibular margin itself will be present and is seen as a “fleck sign” on plain radiographs. • A longitudinal tear of one of the peroneal tendons may result in subluxation of only a portion of the tendon, creating an incarceration of the tear around the posterolateral fibula. The peroneus brevis is relatively flat as it passes through the retromalleolar space and is more commonly involved in this pattern. • Subluxation may occur within the peroneal sheath (intrasheath subluxation) or the tendons may dislocate completely out from behind the fibular. • Some acute peroneal subluxations are missed in the setting of ankle sprains. Complete irreducible dislocations may only be suspected based upon the presence of lateral fullness and peroneal weakness. • Subacute or voluntary subluxation of the tendons may be elicited by having the patient forcibly evert the foot against resistance while simultaneously moving from a plantarflexed to a dorsiflexed ankle position. Marked lateral prominence will result. • Voluntarily induced snapping of the tendons at or above the retromalleolar space may indicate intrasheath subluxation of the peroneal tendons. The tendons dynamically cross over each other within the sheath without passing around the posterolateral corner of the fibula. Most patients can reproduce the snapping with forcible circumduction of the hindfoot. • Internally rotated (mortise) views of the ankle may demonstrate a “fleck sign” indicating avulsion of the insertion of the SPR. • Magnetic resonance imaging (MRI) of the ankle may be very useful in evaluation of peroneal pathology because it allows evaluation of the morphology of the groove (Fig. 29.1) and detection of tears or an accessory peroneus quartus. The false-negative rate, however, is high, and a high index of suspicion must be maintained for subtle longitudinal peroneal tears in patients with associated ankle instability even in the presence of a negative study.2 • Dynamic evidence of peroneal subluxation can be documented through ultrasound or dynamic computed tomography (CT). In practice, MRI is typically preferred as a readily interpretable modality, and these are necessary only when the combination of MRI and clinical examination is equivocal. • True dislocation of the peroneals is best considered a surgical problem. • Historical precedent exists for cast immobilization of relocatable peroneal tendons following an acute trauma. The success rate is less than 50% and the required immobilization will delay rehabilitation of other associated injuries (typically an anterior talofibular ligament [ATFL] tear).3 Cast treatment is recommended only for patients that are poor surgical candidates. • Chronic dynamic posterolateral subluxation of the peroneal tendons eventually leads to further peroneal degeneration as the tendon forcibly passes around the posterior margin of the fibula. Surgical intervention is recommended. • Intrasheath subluxation alone has not been demonstrated to lead to chronic degeneration. The problem may be made more symptomatic by the presence of inflamed tenosynovium. Immobilization, physical therapy, or modalities may be safely attempted as alternative to surgical intervention. Fig. 29.1 Convex peroneal groove (a) before and (b) after (arrow) groove deepening. • Groove deepening is relatively benign and contraindications are minimal. • Care must be exercised if the patient has had a prior tenodesis procedure for augmented lateral ankle ligament reconstruction because the prior bone tunnels may be too extensive to allow a standard trapdoor deepening procedure. • The primary goal of the procedure is to eliminate subluxation of the peroneal tendons around the posterolateral corner of the fibula. • The secondary goal of the procedure is to create a more capacious retromalleolar space, reduce the pressure on the tendons themselves, and eliminate any extraneous sources of impingement that may contribute to pain or intrasheath subluxation.1,4 • A groove deepening procedure utilizing a cortical trapdoor allows for extensive deepening of the retromalleolar groove if necessary. If properly performed, the result is minimal exposure of the tendon to a raw bony surface. • The most common alternative to the trapdoor procedure is the indirect method in which a drill from the distal tip of the fibula is used to remove the cancellous bone underneath the posterior cortex. A tamp is used to forcibly impact the posterior bone.5 The overall degree of dissection is similar to the traditional technique, but any redundancy of the SPR is not as readily addressed. • Simple retinacular repair without groove deepening has also been advocated. Although equivalent results have been reported in small retrospective selected series,6 no randomized controlled prospective trial has compared the two techniques. The secondary benefits of creating space for and reducing pressure on the tendons remain attractive. • Tendoscopic groove deepening with creation of a raw bony surface has been reported,7 but does not allow access to associated peroneal pathology and has significant potential for postoperative adhesion. • Posterior sliding bone block techniques are effective at eliminating subluxation, but have considerable potential for adhesion and do not provide decompression of the tendon in the retromalleolar space.8 They remain a viable option for rare cases with severely dysplastic fibulae. • Adequate decompression of the sheath is mandatory. • Redundancy in the SPR must be eliminated along with any periosteal elevation. • Early motion is always indicated for any peroneal reconstruction. • A bolster is used under the ipsilateral buttock to internally rotate the operative leg. • Thigh tourniquet control is used. • An extensile incision along the peroneal sheath is mandatory because peroneal tears may be encountered extending distally or proximally. MRI alone is not adequate to exclude this possibility. • Chronic ankle instability often coexists with peroneal pathology, and ligament reconstruction may be required. Both sites may be readily addressed with an extensile incision placed over the midline of the fibula. • The critical portion of the SPR is usually visible as a condensation of fibers attaching to the posterior margin of the fibula and beginning at the distal tip (Fig. 29.2). The first 1.5 cm of the sheath is the most mechanically important portion. Open the peroneal sheath below this level with a gentle spreading technique. • The SPR is now divided directly off its posterior attachment to the fibula (Fig. 29.2 inset). If a periosteal pouch and/or an avulsed bony fragment is present, manipulate the tendons back into position and divide the SPR at the site that would be expected to attach to the posterior margin of the bone. • The peroneal tendons are now separately inspected. Table 29.1 provides an algorithm for addressing peroneal pathology in the retromalleolar region. • Excess tenosynovium and peroneus brevis muscle belly extending into the retromalleolar space is excised. If a peroneus quartus is present, it will have a small muscle belly in the sheath and a separate tendon blending into the calcaneal periosteum (Fig. 29.3). It is nonfunctional and should be excised. • The peroneals are now dislocated anteriorly. • A microsagittal saw is used to create a posterior to anterior cut just behind the posterolateral margin of the distal fibula. The cut must extend approximately 5 mm around the tip of the fibula and proximally for 2.5 cm (Fig. 29.4). • Transverse counter cuts are made at the proximal and distal ends of the trapdoor cut (Fig. 29.5). • An 8-mm Hoke osteotome is used to gently crack open the posterior cortex of the fibula, hinging on the uncut medial margin (Fig. 29.6). • A rongeur or burr is used to remove cancellous bone from the posterior fibula as necessary to deepen the groove (Fig. 29.6 inset). • A bone tamp is used to reposition the trapdoor into place (Fig. 29.7). Deepening of at least 4 to 6 mm is typically expected. No fixation is needed; impaction and pressure from the relocated peroneal tendons will be adequate. • Two 0.062 K-wire holes are drilled from the lateral cortex into the groove just posterior to the now-impacted trapdoor of cortical bone. A 2–0 Ethibond suture is used in mattress fashion to advance the previously divided SPR into the groove (Fig. 29.8 and inset). This maneuver covers the raw bone of the overhanging lip of posterolateral fibula and eliminates any redundancy in the SPR itself. • Free gliding of both tendons is confirmed. The remaining proximal portion of the SPR is repaired with 2–0 Vicryl suture.
29.1 Indications
29.1.1 Pathology
29.1.2 Clinical Evaluation
29.1.3 Radiographic Evaluation
29.1.4 Nonoperative Options
29.1.5 Contraindications
29.2 Goals of Surgical Procedure
29.3 Advantages of Surgical Procedure
29.4 Key Principles
29.5 Preoperative Preparation and Patient Positioning
29.6 Operative Technique
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