INTRODUCTION TO PROXIMAL PHALANX EXTENSION OSTEOTOMY

The surgical management of hallux rigidus demands a nuanced understanding of first ray biomechanics and patient-specific kinematic deficits. While isolated dorsal cheilectomy has long been the workhorse for early to moderate hallux rigidus (Coughlin and Shurnas Grades I and II), contemporary evidence suggests that combining cheilectomy with an extension osteotomy of the proximal phalanx (often referred to eponymously as the Moberg osteotomy) yields superior clinical outcomes.

The primary purpose of this operation is to alter the functional arc of motion of the first metatarsophalangeal (MTP) joint. By performing a dorsal, closing wedge osteotomy at the base of the proximal phalanx, the surgeon effectively converts unnecessary plantar flexion into critically needed dorsiflexion. This kinematic shift allows the hallux to clear the ground during the toe-off phase of the gait cycle, significantly reducing dorsal impingement pain and improving overall patient satisfaction compared to isolated cheilectomy.

BIOMECHANICS AND PATHOPHYSIOLOGY

To fully appreciate the utility of the extension osteotomy, one must understand the biomechanical demands placed on the first MTP joint during normal human locomotion.

During the terminal stance and pre-swing phases of gait, the first MTP joint must dorsiflex approximately 65 to 75 degrees to engage the windlass mechanism, stabilizing the medial longitudinal arch. In hallux rigidus, dorsal osteophyte formation and capsular contracture mechanically block this essential dorsiflexion.

The extension osteotomy does not inherently increase the total arc of motion of the diarthrodial joint; rather, it translates the existing arc of motion dorsally. For example, a patient with a preoperative arc of 10 degrees of dorsiflexion and 40 degrees of plantar flexion has a total arc of 50 degrees. By removing a 6-mm dorsal wedge (which typically correlates to approximately 15 to 20 degrees of angular correction), the new functional arc becomes 25 to 30 degrees of dorsiflexion and 20 degrees of plantar flexion. This translated arc is vastly more functional for normal ambulation.

CLINICAL PEARL: Because the osteotomy trades plantar flexion for dorsiflexion, a thorough preoperative clinical assessment is mandatory. The patient must possess a minimum of 15 to 20 degrees of preoperative plantar flexion; otherwise, the procedure may result in a functionally detrimental loss of toe purchase, leading to transfer metatarsalgia.

INDICATIONS AND CONTRAINDICATIONS

Indications

• Symptomatic Hallux Rigidus: Primarily Coughlin and Shurnas Grades I and II, and select Grade III cases where the plantar articular cartilage remains viable.
• Inadequate Dorsiflexion Post-Cheilectomy: Intraoperative assessment revealing less than 60 degrees of dorsiflexion after adequate dorsal cheilectomy.
• Adequate Plantar Flexion: Presence of at least 15 to 20 degrees of active/passive plantar flexion.
• Failed Conservative Management: Persistent pain despite rigid Morton's extensions, rocker-bottom shoe modifications, and intra-articular corticosteroid injections.

Contraindications

• Severe Joint Degeneration: Coughlin and Shurnas Grade IV hallux rigidus (bone-on-bone with pain throughout the entire arc of motion). Arthrodesis is the gold standard here.
• Inadequate Plantar Flexion: Preoperative plantar flexion of less than 10 degrees.
• Inflammatory Arthropathy: Rheumatoid arthritis or severe gouty arthropathy affecting the first MTP joint.
• Severe Osteopenia/Osteoporosis: Poor bone stock that precludes adequate fixation of the delicate proximal phalangeal bridge.

PREOPERATIVE PLANNING

Standard weight-bearing anteroposterior (AP), lateral, and sesamoid axial radiographs of the foot are required. The lateral radiograph is utilized to template the size of the dorsal wedge. Typically, a 6-mm dorsal wedge provides approximately 15 to 20 degrees of dorsiflexion. The surgeon must also evaluate the extent of dorsal metatarsal head osteophytosis to plan the concurrent limited cheilectomy.

SURGICAL TECHNIQUE: THE THOMAS AND SMITH METHOD

The following technique, described by Thomas and Smith, provides a highly reproducible, safe, and biomechanically sound approach to the extension osteotomy of the proximal phalanx.

1. Patient Positioning and Anesthesia

The patient is placed in the supine position on the operating table. The procedure can be performed under general anesthesia, regional anesthesia (popliteal block), or a local ankle block with monitored anesthesia care (MAC). A calf or ankle tourniquet is applied to ensure a bloodless surgical field.

2. Surgical Approach and Exposure

• Incision: Make a longitudinal dorsomedial incision centered over the first MTP joint, extending from the distal third of the first metatarsal to the interphalangeal joint of the hallux.
• Nerve Protection: Carefully dissect through the subcutaneous tissues. Identify, mobilize, and meticulously retract the dorsomedial cutaneous nerve of the hallux. Iatrogenic injury to this nerve can result in painful neuromas or debilitating numbness.
• Capsulotomy: Perform a longitudinal metatarsophalangeal capsulotomy in line with the skin incision. Elevate the capsule via sharp dissection, reflecting it both dorsally and plantarly to expose the metatarsal head and the base of the proximal phalanx.

3. Joint Preparation and Limited Cheilectomy

• Medial Eminence Resection: Using a reciprocating saw, resect 1 to 2 mm of the medial eminence.

  SURGICAL RATIONALE: Resecting a small portion of the medial eminence exposes bleeding cancellous bone, which significantly promotes the healing of the capsule to the bone after final closure, reducing the risk of postoperative capsular dehiscence.

• Limited Dorsal Cheilectomy: Resect the dorsal osteophytes and the dorsal portion of the distal first metatarsal using a power sagittal saw.

  CLINICAL PEARL: In the context of a concurrent extension osteotomy, this cheilectomy is limited. The resection is less aggressive than the amount removed during a traditional, isolated cheilectomy. The surgeon does not need to aggressively resect the metatarsal head to achieve 60 degrees of dorsiflexion relative to the weight-bearing surface, as the phalangeal osteotomy will provide the remaining necessary functional clearance.

• Osteophyte Debridement: Inspect the lateral aspects of the metatarsal head and the base of the proximal phalanx. Resect any peripheral osteophytes that may impinge during the functional arc of motion.

4. Protecting the Flexor Hallucis Longus (FHL)

Identify the flexor hallucis longus (FHL) tendon plantarly. The FHL is at extreme risk during the plantar-ward progression of the saw blade during the osteotomy. Meticulous subperiosteal dissection along the plantar aspect of the proximal phalanx is required to place a protective retractor (such as a small Hohmann or Freer elevator) between the bone and the tendon.

5. The Osteotomy Marker (Critical Step)

• Place a 0.062-inch Kirschner wire (K-wire) transversely from medial to lateral across the base of the proximal phalanx.
• This wire must be placed parallel to, and as close to, the articular surface of the proximal phalanx as possible without penetrating the joint capsule or the cartilaginous surface.

  SURGICAL WARNING: The placement of this 0.062-inch K-wire is the most critical step in preventing an inadvertent intra-articular fracture. It serves as a physical, tactile marker and a backstop for the saw blade during the proximal osteotomy cut.

6. Executing the Closing Wedge Osteotomy

• The Proximal Cut: Using an oscillating saw equipped with a fine 0.5-mm blade, initiate the proximal osteotomy immediately along the distal surface of the 0.062-inch K-wire.
• Stability Control: Do not complete this first osteotomy through the plantar cortex yet. Leaving the plantar cortex intact maintains the structural stability of the phalanx, making the second cut significantly easier and more precise.
• The Distal Cut: Make the second cut distal to the first, angling it obliquely in a proximal direction to intersect the first cut just dorsal to the plantar cortex. This oblique cut is designed to remove a measured 6-mm dorsal wedge of bone.
• Remove the dorsal wedge of cancellous bone and verify the geometry of the osteotomy.

7. Managing the Plantar Cortex

• To close the osteotomy, the plantar cortex must act as a hinge. However, the plantar cortex of the proximal phalanx is thick and prone to uncontrolled displacement if simply forced closed.
• Weakening the Cortex: Use a 1.5-mm drill bit to create multiple unicortical holes into the plantar cortex at the apex of the osteotomy.

  SURGICAL RATIONALE: Drilling these holes weakens the plantar cortex, allowing for a controlled "greenstick" fracture when the osteotomy is closed. Furthermore, using a drill rather than a saw to breach the plantar cortex drastically reduces the risk of iatrogenic laceration to the underlying FHL tendon.

8. Reduction and Fixation

• Manually close the osteotomy by dorsiflexing the distal phalanx. Ensure that the bony surfaces appose flushly without gapping.
• Drill Holes for Fixation: While maintaining reduction, prepare for wire fixation. Start the proximal drill hole just adjacent to the articular cartilage at the base of the proximal phalanx, approximately 2 to 3 mm proximal to the osteotomy line.

  PITFALL AVOIDANCE: Drilling too close to the osteotomy edge will result in the wire cutting through the fragile cancellous bone bridge (breaking the suture tunnel), leading to loss of fixation.

• Wire Passage: Pass a 3-0 stainless steel wire through the 1.5-mm drill holes at the dorsomedial aspect of the osteotomy.
• Tensioning: Pass the wire from proximal to distal. When tightening the wire, place the majority of the tension on the distal side of the construct. The proximal bone bridge is delicate; excessive proximal tension will fracture the hole. Twist the wire securely, cut the excess, and bury the knot into the adjacent soft tissue to prevent hardware prominence and skin irritation.

(Note: While Thomas and Smith describe 3-0 wire fixation, modern variations may utilize low-profile titanium staples, headless compression screws, or specialized osteotomy plates depending on surgeon preference and bone quality. However, wire fixation remains highly cost-effective and biomechanically sufficient for this metaphyseal region).

9. Closure

• Irrigate the wound copiously with sterile saline to remove bone debris.
• Repair the MTP joint capsule using 2-0 or 3-0 absorbable sutures. The previously resected medial eminence will provide an excellent bleeding bone bed for capsular adherence.
• Close the subcutaneous tissue and skin in a standard layered fashion. Apply a sterile, mildly compressive dressing.

POSTOPERATIVE REHABILITATION PROTOCOL

The postoperative protocol is designed to protect the osteotomy while encouraging early motion to prevent capsular scarring.

Weeks 0 to 2

• Weight-Bearing: The patient is placed in a rigid postoperative shoe or a controlled ankle motion (CAM) boot. Heel-weight-bearing only is permitted to protect the osteotomy site from excessive bending moments.
• Wound Care: The initial surgical dressing remains intact until the first postoperative visit at 10 to 14 days, at which point sutures are removed.
• Elevation: Strict elevation is encouraged to minimize edema and promote wound healing.

Weeks 2 to 6

• Weight-Bearing: Transition to flat-foot weight-bearing in the rigid postoperative shoe.
• Physical Therapy: Active and passive range of motion (ROM) exercises of the first MTP joint are initiated. The focus is on maximizing dorsiflexion. Plantar flexion exercises are also introduced to prevent contracture of the dorsal capsule.
• Radiographic Assessment: AP and lateral radiographs are obtained at 4 to 6 weeks to assess for callus formation and osteotomy consolidation.

Weeks 6 and Beyond

• Shoe Wear: Once clinical and radiographic union is confirmed (typically around 6 to 8 weeks), the patient may transition into a stiff-soled athletic shoe with a wide toe box.
• Activity: High-impact activities and sports are gradually reintroduced between 10 and 12 weeks, guided by patient comfort and the restoration of normal gait mechanics.

COMPLICATIONS AND MANAGEMENT

While the extension osteotomy of the proximal phalanx is highly successful, surgeons must be prepared to navigate potential complications:

1. Intra-articular Fracture: The most devastating technical error is allowing the saw blade to breach the proximal articular surface. This is mitigated by the strict use of the 0.062-inch K-wire marker. If a fracture occurs, it must be anatomically reduced and fixed with micro-screws, and the patient's weight-bearing status must be delayed.
2. Flexor Hallucis Longus Laceration: Aggressive sawing through the plantar cortex can sever the FHL. Utilizing the drill-hole greenstick technique and placing a protective plantar retractor are mandatory preventative steps.
3. Hardware Prominence: The dorsal skin over the hallux is thin. A poorly buried wire knot or a prominent screw head can cause severe shoe-wear irritation, necessitating hardware removal after bony union is achieved.
4. Undercorrection / Overcorrection: Removing an inadequate wedge will fail to relieve dorsal impingement. Conversely, removing too large a wedge (overcorrection) will result in a "cock-up" deformity of the hallux, leading to loss of toe purchase and secondary transfer metatarsalgia. Precise preoperative templating and intraoperative assessment are paramount.
5. Nonunion / Delayed Union: Rare in the highly vascular metaphyseal bone of the proximal phalanx, but possible in patients with poor compliance, severe osteopenia, or nicotine use. Management includes prolonged immobilization and, if symptomatic, revision with bone grafting and rigid internal fixation.

CONCLUSION

The extension osteotomy of the proximal phalanx represents a sophisticated, biomechanically sound intervention for the treatment of symptomatic hallux rigidus. By meticulously executing the Thomas and Smith technique—specifically the use of a K-wire backstop, the limited cheilectomy, and the controlled greensticking of the plantar cortex—orthopaedic surgeons can safely shift the functional arc of motion. This joint-sparing procedure not only alleviates dorsal impingement but also restores the critical kinematics required for a pain-free, efficient gait cycle.