Autologous Osteoligamentous Reconstruction of Scaphoid Proximal Pole With Metatarsal Head and Collateral Ligament: Cadaver Anatomic Description of Novel Surgical Technique

Abstract

Background: Historically, scaphoid nonunion has been surgically treated with vascularized bone graft taken from multiple different anatomic sites. However, none of these grafts fully recapitulate the unique osteoligamentous anatomy of the proximal pole of the scaphoid and the attachment of the scapholunate ligament (SLIL). We studied the anatomy of the vascularized second metatarsal head with its lateral collateral ligament as a potential novel treatment of proximal pole scaphoid nonunion with collapse. Methods: Scaphoids and second metatarsal heads were harvested from bilateral upper and lower extremities of 18 fresh frozen cadavers (10 male, 8 female) for a total of 36 scaphoids and 36 second metatarsal heads. The ipsilateral second metatarsal head was harvested with its lateral collateral ligament and its blood supply from the second dorsal metatarsal artery (SDMA). Measurements of the scaphoid, the SLIL, the second metatarsal head, and lateral collateral ligaments were compared to matched limbs from the same cadaver. Results: The anatomic dimensions of the second metatarsal head with its lateral collateral ligament are similar to the scaphoid proximal pole and the SLIL in matched cadaveric specimen. Conclusions: This anatomic cadaver study reveals that the second metatarsal head with its associated lateral collateral ligament is a well-matched donor to reconstruct the proximal pole of the scaphoid and SLIL. This anatomic similarity may be well suited to treat nonunion of the scaphoid proximal pole with or without avascular necrosis with simultaneous reconstruction of the SLIL. The authors describe a technique of vascularized reconstruction of the osteoligamentous proximal pole of the scaphoid with its attached SLIL utilizing autologous second metatarsal head with its attached lateral collateral ligament. Based on this cadaver study, this technique merits consideration.

Introduction

Fractures of the proximal pole of the scaphoid are at known risk for nonunion as a result of the distally based vascular supply to the scaphoid and technical difficulty of obtaining rigid fixation of a diminutive bone fragment.^1-5 Multiple different surgical options have been described to address this difficult problem of proximal pole nonunion. None of these have emerged as the universally accepted gold standard.

These options include nonvascularized bone grafts such as rib graft^6,7 to replace the proximal pole, or to augment rigid fixation with cancellous bone graft in the setting of a vascularized proximal pole. When there is avascular necrosis of the proximal pole, vascularized bone grafts are potentially indicated. These include pedicled bone flaps from the distal radius^2,5 or free flap reconstruction using the medial femoral trochlea.^8-10

The free medial femoral trochlea bone flaps have resulted in union at rates of near 100%, ¹¹ and rib grafts have also healed with good success.^6,7 Although the concept of “overstuffing” the scaphoid proximal pole with medial femoral trochlea shows promise in elegant cadaver studies, ⁹ the longitudinal outcomes of effectively replacing the osteoligamentous proximal pole of the scaphoid with an oversized osteocartilaginous construct have not been demonstrated.

None of these options completely recapitulate the ligamentous attachments of the proximal pole with a vascularized osteoligamentous construct. In this study, the authors present a cadaver study of the characteristics of a vascularized second metatarsophalangeal (MTP) joint with its collateral ligament to reconstruct a scaphoid proximal pole and the SLIL.

The MTP joint anatomy has been described ¹² and found to be effective as a vascularized joint for transfer in upper extremity reconstructions including the sternoclavicular joint ¹³ and the distal radioulnar joint. ¹⁴ Given the properties of a stout collateral ligament attached to a small osteocartilaginous fragment, the MTP joint is an excellent potential donor site for the complex problem of scaphoid proximal pole nonunion from avascular necrosis.

Previous cadaveric biomechanical studies of the MTP joint reveal peak load to failure (ligament rupture) is 110 N at a rate of 5 mm/min. ¹⁴ This is comparable to previous studies of the scapholunate ligament (SLIL) peak load to failure which ranges from 62 to 185 N.^15-19

Methods

Cadaveric Dissection

Dissection was performed in 18 fresh cadavers with no prior traumatic injury to the wrist or MTP joints. The cadavers were obtained through the Bulverde Spring Branch Fire and Medical Services facility in accordance with institutional policies. The average specimen age was 72.53 years with 10 male and 8 female specimens. Although there was no traumatic injury to the joints, arthritis was apparent in the majority of second metatarsal heads and scaphoid proximal poles.

Proximal row carpectomy was performed bilaterally in the fresh cadaveric wrists via standard dorsal approach, with careful identification of the scapholunate ligament and preservation of the scaphoid. The SLIL was sharply incised along the radial aspect of the lunate to allow accurate measurement of SLIL thickness.

The ipsilateral second MTP joint was harvested with identification and preservation of the lateral collateral ligament and second metatarsal artery. Access incision was made directly over the second metatarsal. The anterior perforating branches from the plantar digital arteries and nerve branches were identified and dissected, with care taken to preserve the first webspace digital neurovascular bundle. ¹² The second MTP joint was exposed and removed in its entirety with the sagittal saw, dividing the distal metatarsal head from the neck, maintaining the lateral collateral ligament attachment and blood supply. After excision of the MTP joint, the lateral collateral ligament was sharply elevated partially to increase its mobility while maintaining the majority of its insertion.

After harvest, the scaphoid proximal pole was compared to the exposed metatarsal head to assess for an appropriately matched fit (Figure 1). The scaphoid proximal pole with its attached SLIL was removed with a sagittal saw. Preparation of the lateral aspect of the metatarsal head was performed with sagittal saw by longitudinally cutting the metatarsal head just proximal to the lateral collateral ligament insertion (to approximate the scaphoid proximal pole), while preserving the lateral collateral ligament and vascular supply. Prior to reconstruction and fixation, measurements of the scaphoid, SLIL, metatarsal, and MTP collateral ligaments were obtained with a digital caliper.

Figure 1.

Dorsal view of scaphoid attached to second metatarsal head.

Osteoligamentous Construct

The prepared segment of the lateral aspect of the longitudinally cut metatarsal head and lateral collateral ligament complex with associated vasculature was oriented to reconstruct the surgically removed scaphoid proximal pole with its attached dorsal band of the SLIL (Figure 2). Orientation of the metatarsal head was preserved with its dorsal aspect corresponding to the dorsal aspect of the scaphoid proximal pole. Fixation of the osteoligamentous construct was obtained with 0.062 in Kirschner wire fixation. Burr was used to contour the metatarsal head and prevent potential impingement on the capitate.

Figure 2.

Scaphoid attached to second metatarsal head and associated attachments of lateral collateral ligament with vasculature.

Statistical Analysis

Data from the scaphoid and MTP joints were analyzed with a paired 2-sample t-test with a significance level of α = 0.05.

Results

Mean diameter of scaphoid proximal pole was found to be 16.84 ± 1.68 mm, in comparison with the second metatarsal head diameter which was 15.77 ±1.25 mm. Mean width of the SLIL was 3.40 ± 0.86 mm in contrast to mean width of the lateral collateral ligament of 5.14 ± 0.65 mm. Mean ligament thickness of the SLIL was 1.81 ± 0.49 mm and of the lateral collateral ligament was 1.07 ± 0.32 mm. See Table 1.

Table 1.

Measurements of Schaphoid and Second Metatarsal Head.

Mean diameter	Scaphoid proximal pole	16.84 ± 1.68 mm	P < .001
	Second metatarsal head	15.77 ± 1.25 mm
Mean width	Scapholunate ligament	3.40 ± 0.86 mm	P < .001
	Lateral metatarsal collateral ligament	5.14 ± 0.65 mm
Mean thickness	Scapholunate ligament	1.81 ± 0.49 mm	P < .001
	Lateral metatarsal collateral ligament	1.07 ± 0.32 mm

Discussion

Management of scaphoid proximal pole fractures acutely is technically challenging because of the small bone available for rigid fixation. When avascular nonunion of a scaphoid proximal pole ultimately develops, there is difficulty in reconstruction of this mostly cartilaginous structure with poor blood supply and its attached SLIL. Although there is some controversy as to whether vascularized or nonvascularized bone graft reconstruction results in higher union rates, ¹ it is generally accepted that vascularized tissue is desirable to reconstruct a poorly vascularized fracture site with retrograde vascular supply such as the scaphoid.^2,5,8-10 None of the current vascularized reconstructions of the proximal pole of the scaphoid recapitulates the anatomy of the SLIL.^{1,2,5,8-11,20} The medial femoral trochlea flap successfully reconstructs the cartilage of the proximal pole of the scaphoid, but relies on expansion of the normal dimensions of the scaphoid to restore carpal alignment. ⁹ This maintenance of scapholunate integrity without ligament reconstruction with “overstuffing” has been demonstrated in cadavers, ⁹ and in short-term follow-up in the clinical setting.^8,10 The long-term outcomes of “overstuffing” the proximal pole of the scaphoid have not been demonstrated. Theoretically, utilizing the second MTP lateral collateral ligament to reconstruct the scapholunate ligament would decrease the risk for dorsal intercalated segmental instability (DISI) progressing to scapholunate advanced collapse (SLAC) wrist, thus preserving the normal kinematic relationship between the radioscaphoid articulation.

This anatomic cadaver study reveals that the metatarsal head with its associated lateral collateral ligament is a well-matched donor to reconstruct the proximal pole of the scaphoid and scapholunate ligament. This novel application of a known established donor site for vascularized joint transfer is well suited to treat nonunion of the scaphoid proximal pole with avascular necrosis. Although some anatomic differences were observed between donor and recipient tissues, these differences have the theoretical advantage from a technical standpoint, as they would result in a slightly smaller construct that articulates with the lunate without difficulty. Future cadaveric studies would need to be examined to verify the biomechanical advantage of the smaller construct with reconstructed SLIL.

This study has several limitations. As a cadaver study, there is no clinical outcome data to guide recommendations. Donor site morbidity, which is a critical factor to consideration in autologous reconstructions, cannot be assessed in a cadaver study. This study acknowledges that there were some degenerative changes within the specimens harvested from the cadavers as the average age of each cadaver was 72 years. The technique that is proposed would not be performed on patients who have degenerative changes occurring within the proximal pole of the scaphoid but should be indicated for patients who have avascular necrosis of the proximal pole.

Another limitation of this study is that the radius of curvature was not measured or compared for the proximal pole of the scaphoid with respect to the second metatarsal head. Implanting a second metatarsal head in vivo may result in unanticipated kinematic alterations with associated consequences.

This study does not present radiographic representations of the reconstructions, as it is presumed that after reduction of the scaphoid and vascularized osteoligamentous construct, it would be secured with suture anchor fixation into the lunate in the clinical setting. While biomechanical studies were not performed as a part of this study, the strength of the MTP joint with its capsuloligamentous attachments has been shown to be in the range of most studies of biomechanical strength of the SLIL.^{11,14-16,18,19}

Further clinical study is required to determine if the addition of the lateral collateral ligament in the vascularized transfer of the metatarsal head reconstruction of the proximal pole and SLIL maintains normal carpal kinematics clinically in the long term.