Surgical reconstruction of posterior tibial tendon dysfunction: Prospective comparison of flexor digitorum longus substitution combined with lateral column lengthening or medial displacement calcaneal osteotomy

Abstract

Posterior tibial tendon dysfunction (PTTD) may require surgical intervention when nonoperative measures fail. Different methods of bony reconstruction may supplement tendon substitution. This study compares two types of bony procedures used to reinforce reconstruction of the posterior tibial tendon—the lateral column lengthening (LCL), and the medial displacement calcaneal osteotomy (MDCO). Twenty patients with PTTD were evaluated before and after scheduled reconstruction comprised of either flexor digitorum longus (FDL) substitution combined with MDCO (MDCO group, 14 patients) or FDL substitution with LCL fusion or osteotomy (LCL group, 6 patients). Foot/ankle kinematics and temporal–spatial parameters were analyzed using the Milwaukee Foot Model, and results were compared to a previously evaluated normal population of 25 patients. Post-operatively, both patient groups demonstrated significantly improved stride length, cadence and walking speed, as well as improved hindfoot and forefoot position in the sagittal plane. The LCL group also demonstrated greater heel inversion. All post-operative subjects revealed significant improvement in the talo-MT1 angle in the A/P and lateral planes, calcaneal pitch and medial cuneiform-MT5 height. Surgical reconstruction of PTTD with either the LCL or MDCO shows comparable improvements in gait parameters, with better heel inversion seen with the LCL, but improved 1st ray plantarflexion and varus with the MDCO. Both procedures demonstrated comparable improvements in radiographic measurements.

Introduction

The tibialis posterior muscle serves as the primary inverter of the heel and is active from mid-to-terminal stance. Its contraction allows the gastrocnemius–soleus complex to shift to the medial side of the subtalar axis; when the gastrocnemius–soleus contracts, it then becomes a powerful heel inverter. Heel inversion creates obliquity of the transverse tarsal (talo-navicular, calcaneo-cuboid) joint, thereby creating a rigid midfoot during terminal stance, which allows efficient transfer of stored energy in the lower extremity for toe-off and swing phase. Dysfunction of the tibialis posterior muscle results in less efficient gait, as the heel does not effectively medialize upon tibialis posterior contraction, and the gastrocnemius–soleus complex requires greater excursion to initiate heel inversion. In cases where the tibialis posterior muscle no longer contracts, resting heel valgus may be accentuated as the gastroc-soleus complex becomes a deforming force, and its subsequent contraction creates an external valgus moment on the heel. In these cases, the supporting medial soft tissues become attenuated, further accentuating the resultant flatfoot deformity. Late changes with the pathologic flatfoot include lateral hindfoot bony impingement, sinus tarsi inflammation, peroneal tendonitis, equinus contracture, and eventual arthrosis.

Posterior tibial tendon dysfunction (PTTD) was first classified by Johnson and Strom [1] with later modification by Myerson [2]. Stage I PTTD involves inflammation of the tendon with no functional deficiencies. The hindfoot remains supple, and patients are able to perform both double and single heel raises. In stage II PTTD, the hindfoot remains supple, as indicated by the ability to perform a double heel raise; however, patients are not able to perform a single heel raise, indicative of an incompetent tendon. The tendon may remain intact, but is no longer able to adequately contract. With stage III PTTD, the tendon is incompetent and the hindfoot rigid, which is indicative of arthrosis. The patient is not able to invert the heel with a double heel raise. Stage IV dysfunction exhibits additional deltoid ligament incompetence, resulting in varus tilt of the talus within the ankle mortise [11]. More recently, a stage IIb has been described [3]. In this population, the heel is brought to a neutral position, but the midfoot remains in greater than 10° varus, with residual elevation of the medial column.

When PTTD cannot be appropriately addressed through conservative measures (rest, rehabilitation, and/or bracing), surgical intervention is necessary to correct the resulting deformity and restore function of the limb. Currently, most surgeons perform reconstruction/substitution of the dysfunctional posterior tibial tendon (PTT) with transfer of the flexor digitorum longus (FDL) into the navicular tuberosity [4]. Additional soft tissue reconstructive procedures include repair/imbrication of the spring ligament and/or the talo-navicular capsule. In cases with concomitant equinus contracture, either a gastrocnemius recession or tendoAchilles lengthening (TAL) is indicated. While soft tissue reconstruction has been shown to alleviate pain, residual pes planovalgus and midfoot abduction frequently remain [5]. The medial displacement calcaneal osteotomy (MDCO) provides both static and dynamic correction by medialization of the calcaneal insertion of the gastroc-soleus complex, thereby allowing for initiation of heel inversion by the PTT and more effective function of the gastroc-soleus complex as a powerful secondary heel inverter. The MDCO has been shown to improve patients’ function and radiographic parameters [6], [7], [8], [9]. Similarly, other authors have recommended the use of lateral column lengthening (LCL), either through the anterior neck of the calcaneus, or with lateral column lengthening fusion (LCLF) of the calcaneo-cuboid joint, for correction of pes planovalgus and midfoot abduction [10], [11], [12], [13]. Comparable patient satisfaction and radiographic improvement have been noted with this technique. No published study has compared these different osteotomies for the surgical treatment of PTTD.

The development of multisegmental foot and ankle models has allowed for more precise quantitative clinical assessment of pathologic gait [14], [15], [16], [17], [18], [19], and recent application of such models in patients with PTTD have demonstrated a powerful capacity for characterization of the pathology [20], [21], [22], [23], [24], [25]. It was the intent of this study to extend these multisegmental kinematic measures to a post-operative population and compare outcomes from two different surgical procedures.

This is a follow-up study to a previous characterization of patients with PTTD who were assessed prior to surgical intervention [26]. In this study, 20 patients with PTTD underwent either reconstruction/substitution of the PTT with an FDL tendon transfer combined with MDCO (“MDCO group”), or PTT/FDL reconstruction combined with MDCO and lateral column lengthening through the anterior neck of the calcaneus or calcaneo-cuboid lengthening fusion (“LCL group”) [4]. Both populations were compared to a previously assessed healthy population (13 males, 12 females; 41.3 ± 12.5 years) [27], [28]. Additional radiographic evaluations were performed to measure correction of pre-operative pes planovalgus and abduction deformities. We hypothesized that both procedures would provide comparable improvements in temporal–spatial parameters, but that patients receiving lateral column lengthening (LCL group) would demonstrate more inversion post-operatively compared to the MDCO group.