The Adaptive Proximal Scaphoid Implant: Long-Term Follow-Up

Abstract

Background:

Scaphoid proximal pole fracture with avascular necrosis is a surgical challenge, particularly in patients with high functional demand. An option is the pyrocarbon adaptive proximal scaphoid implant (APSI), replacing the necrotic proximal pole.

Methods:

A long-term follow-up study of the early cases treated in our department was conducted. Thirty-six patients with a median follow-up time of 19 years (range, 11-25) were included in the analysis, performing clinical and radiological evaluations.

Results:

Clinically, significant improvements were observed in mean pain Numeric Rating Scale (from 6.8 [SD 2.1] to 2 [2]), range of motion, grip strength measured with the Jamar dynamometer (from 18 [8] kg to 24 [9] kg), Disabilities of the Arm, Shoulder, and Hand score (from 66 [6.5] to 13.7 [6.4]), and Patient-Rated Wrist Evaluation score (from 73 [10] to 28 [12]). Radiographs showed good implant stability. No patient required implant removal.

Conclusion:

The APSI prosthesis proves effective long term in relieving pain, improving function, and preventing carpal collapse through stable biomechanical integration.

Introduction

The management of proximal pole scaphoid nonunion including scaphoid nonunion advanced collapse (SNAC wrist) remains a challenging issue for hand surgeons. These lesions result in a progression of disability in wrist function. ¹

The most commonly performed procedure for the treatment of scaphoid nonunion (and early-stage SNAC wrist) ² is open reduction and internal fixation using a nonvascularized bone graft. ³ Alternatively, vascularized bone grafts can be used.^4-6 When reconstruction of the necrotic pole is not feasible and carpal alignment cannot be restored (mid- to advanced-stage SNAC wrist), salvage procedures are indicated. Prosthetic replacement of the scaphoid has emerged as a less-invasive alternative to more traditional salvage techniques, such as partial scaphoidectomy, proximal row carpectomy, or four-corner fusion.^7-10

Numerous implants and prostheses have been developed. The adaptive proximal scaphoid implant (APSI) (Tornier SAS Etablissement BIOProfile, Grenoble Cedex, France) is a pyrocarbon partial scaphoid prosthesis, ovoid in shape and nonfixed, designed to function as a dynamic spacer by replacing the proximal pole of the scaphoid. The APSI preserves mobility of the proximal carpal row and restores carpal geometry, thereby preventing progression of SNAC. ¹¹ Clinical studies have reported high levels of patient satisfaction, with 88% demonstrating favorable outcomes, including good grip strength recovery and early return to work and sports activities. ¹¹

The aim of our study is to evaluate the long-term clinical and radiographic outcomes of APSI implantation for the treatment of scaphoid proximal pole nonunions and SNAC wrist, with particular focus on wrist function, including pain, range of motion (ROM), strength, and performance in daily activities.

Methods

This single-center retrospective study analyzed 88 patients who underwent APSI implantation between 2000 and 2016 at the University Hospital of Verona, Italy. The inclusion criteria were as follows: a diagnosis of stage II or III SNAC, according to the Vender classification; ¹² no history of prior open surgical procedures for the treatment of SNAC, including the absence of any previous dorsal surgical approach to the wrist (in order to avoid an evaluation bias during follow-up related to prior surgical aggression of the articular tissues); a minimum follow-up period of 8 years; and a history of exclusively percutaneous treatment with Kirschner wires (provided that the procedure had been completed and the wires removed prior to enrolment) or percutaneous screw fixation. Exclusion criteria included diagnosis of stage I SNAC and history of attempted open reduction and internal fixation. All APSI implantation procedures were performed by the same surgeon (MC, expert level 5 according to Tang and Giddins), ¹³ and follow-up evaluations were carried out by the same surgical team. The study was approved by the local ethics committee. All patients provided written informed consent for the use of their data in this study. Withdrawal of consent or patient death was considered as an exclusion criterion.

Assessment

All patients underwent the following assessments: wrist anteroposterior and lateral radiographs performed within the last 3 months; pain assessment using the Numeric Rating Scale (NRS); measurement of wrist ROM in flexion-extension and radial-ulnar deviation; grip strength using a Jamar dynamometer ¹⁴ ; and assessment of functional limitations in daily activities using the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire (minimum score: 0—no limitation; maximum score: 100—complete limitation) ¹⁵ and the Patient-Rated Wrist Evaluation (PRWE) questionnaire (minimum score: 0—no limitation; maximum score: 100—complete limitation). ¹⁶ These assessments were part of the standard preoperative evaluation routinely conducted for all patients. Long-term follow-up included a comparative analysis of preoperative and postoperative parameters. All eligible patients were recalled for clinical evaluations and wrist radiographs. Follow-up duration varied according to the date of implantation.

Surgical Technique

Surgical procedures were performed under regional anesthesia using axillary nerve block, with the application of a pneumatic tourniquet following limb exsanguination. Preoperative antibiotic prophylaxis was administered in accordance with local institutional guidelines. A longitudinal incision was made, centered over the radiocarpal joint between the second and third extensor compartments. The extensor retinaculum was incised, followed by opening of the third compartment and displacement of the extensor pollicis longus tendon. The terminal branch of the posterior interosseous nerve was identified, isolated, and cauterized. Dissection was then extended distally to reach the dorsal radiocarpal ligaments. The joint capsule was incised dorsally, following the Berger et al ¹⁷ capsular flap technique. This approach provided adequate exposure of the scaphoid and the radiocarpal joint.

In all cases, a radial styloidectomy was performed. The proximal pole of the scaphoid was resected using a scalpel. The resection plane was oriented perpendicular to the frontal axis of the scaphoid and parallel to the frontal slope of the distal radius on lateral view. The extent of resection was tailored to the degree of osteochondral involvement of the scaphoid’s proximal pole. During resection, particular care was taken to identify and preserve the dorsal intercarpal ligament. Implant size (small, medium, or large) was selected intraoperatively using trial components under fluoroscopic guidance, by evaluating wrist motion through flexion-extension and radioulnar deviation. Once the appropriate implant size was selected, the APSI was positioned without excessive tension, ensuring adequate mobility and adaptability to wrist movements. ⁷ It is important to emphasize that the APSI prosthesis functions as a dynamic interpositional spacer within the proximal carpal row, due to its lack of fixation to either ligamentous or osseous structures. Implant stability and correct positioning were verified under fluoroscopic guidance. Following prosthetic implantation, the joint capsule was sutured with a slowly absorbable monofilament suture (PDS^TM suture 4-0, Ethicon, Johnson and Johnson, New Brunswick, New Jersey). In cases of dorsal intercalated segment instability (DISI) deformity, a dorsal capsuloligamentous reinforcement using the radio-lunate-triquetral ligament was performed by directly suturing the capsuloligamentous tissue, as described by Berger et al. ¹⁷ The operation was concluded with closure of the extensor retinaculum and skin.

Postoperatively, all patients followed the same standardized rehabilitation protocol. A custom-molded anterior forearm-to-metacarpal fiberglass splint was applied immediately after surgery, with the wrist positioned in a neutral alignment. The splint was maintained continuously for 3 weeks, with weekly dressing changes and suture removal at 2 weeks. During the immobilization period, patients were instructed to maintain active digital mobility. Upon splint removal, a physiotherapy program was initiated to progressively restore wrist flexion-extension and to strengthen the surrounding musculature. During this phase, patients were advised to wear a rigid wrist brace at night. Physiotherapy continued for approximately 6 to 8 weeks, depending on individual recovery, with a gradual return to activities of daily living. Follow-up radiographs were performed 1 month after operation. Patients were instructed to avoid strenuous activities or heavy lifting (eg, cycling or weights over 10 kg) for a total of 3 months.

Statistical Analysis

Statistical methods were selected according to the distribution characteristics of the data, which were verified using the Shapiro-Wilk normality test. Continuous variables were summarized as mean and standard deviation when normally distributed, and as median with interquartile range (IQR) when the distribution was nonnormal. Comparisons between groups were performed using the paired Student’s t-test for normally distributed data, and the Wilcoxon signed-rank test for nonnormally distributed data. A P-value of less than .05 was considered indicative of statistical significance.

Results

Of the 88 patients analyzed, 39 (44%) had previously undergone open reduction and internal fixation with a headless screw, 7 (8%) had been treated with other fixation methods or through a palmar approach, 2 (2%) died during the follow-up period, and 4 (5%) were lost to follow-up. Thirty-six patients who had received APSI with a median follow-up time of 19 (IQR 8.3; range 11-25) years were included in the study according to the inclusion criteria. Twenty-nine were men (81%). The median age at the time of surgical treatment was 32 (IQR 9; range 27-65) years, and 30 of them underwent surgery on the dominant side. Twenty-four patients had no history of previous surgical intervention, whereas 7 had previously undergone percutaneous fixation using Kirschner wires, and 5 had undergone percutaneous screw fixation.

All variables were found to be normally distributed, except for patient age, the time between surgery and long-term follow-up, and the long-term ulnar deviation ROM, NRS, and DASH scores. Outcome data are summarized in Table 1. There was a significant increase in range-of-movement measurements and grip strength at long-term follow-up compared with preoperative measurements. One patient reported an increase in flexion ROM greater than 10°, whereas 11 patients reported changes within ±10° compared to the previous follow-up. Ten patients showed a slight decrease (less than 5°) in radial deviation ROM. Conversely, all patients demonstrated improvement in extension and ulnar deviation ROM. For subjective outcomes, significant improvements were observed in the mean pain NRS, DASH, and PRWE scores. A single patient reported worsening pain (from 5 to 7 on the NRS), while in 5 patients, the improvement was limited, with persistent pain at long-term follow-up (5-6 on the NRS). All patients showed improvement in both the DASH and PRWE scores. No cases of deep or superficial infection were recorded. No patients required implant removal.

Table 1.

Variables Recorded at Preoperative Assessment and Long-Term Follow-Up in 36 Patients Who Received APSI, With a Median Follow-Up of 19 Years (IQR 8.3; Range 11-25).

Variable	Preoperative	Long-term	P-value
Wrist range of:
Flexion	54° (6, 52 to 56)	67° (8, 64 to 69)	<.001
Extension	48° (3, 47 to 49)	65° (4, 64 to 67)	<.001
Ulnar deviation	17° (3, 17 to 18)	* 26° (2.5, 25 to 26)	<.001
Radial deviation	6° (3, 5 to 7)	9° (3, 8 to 10)	<.001
Pain NRS	6.8 (2.1, 6.1 to 7.6)	* 2 (2, 2.3 to 3.4)	<.001
Grip strength (Kg)	18 (8, 16 to 21)	24 (9, 22 to 31)	<.001
DASH score	66 (6.5, 64 to 68)	* 13.7 (6.4, 13 to 17)	<.001
PRWE score	73 (10, 70 to 77)	28 (12, 24 to 32)	<.001

Data are presented as mean (SD, 95% confidence intervals) if normally distributed, and as median (interquartile range [IQR], 95% confidence intervals) if not normally distributed (marked with *). APSI = adaptive proximal scaphoid implant; NRS = Numeric Rating Scale; DASH = Disabilities of the Arm, Shoulder, and Hand; PRWE = Patient-Rated Wrist Evaluation.

Long-term radiographic evaluation confirmed correct positioning of all implants, with no significant damage to surrounding bone structures. However, a general pattern of moderate progression of wrist osteoarthritis and osteolysis (mainly involving the capitate) was observed in all patients. Among those with follow-up exceeding 15 years (24 patients), 5 patients developed lunocapitate osteoarthritis (Figure 1), although grip strength and functional outcomes remained preserved. None of the patients developed severe carpal bone degeneration or high-grade wrist osteoarthritis. In one case, notching of the proximal pole of the capitate was observed, although it was not associated with pain (Figure 2). In another patient, 17 years after APSI implantation, radiocarpal impingement pain was identified, and a second radial styloidectomy was scheduled, resulting in symptomatic improvement. No other patient underwent additional surgical procedures. None of the patients had to change their occupation after surgery, although about half reported minor adaptations in work tasks due to residual stiffness or mild discomfort.

Figure 1.

Clinical case (1). Radiographs of a 37-year-old male construction worker with scaphoid nonunion of the right wrist following an untreated scaphoid fracture (a); postoperative follow-up after adaptive proximal scaphoid implant implant placement and minimal styloidectomy, with anterior fiberglass splint still in place (b); 4-year follow-up (c); 18-year follow-up showing progression of lunocapitate osteoarthritis, minimally symptomatic (d); clinical appearance at 18-year follow-up (e).

Figure 2.

Clinical case (2). Radiographs of a 31-year-old male manual worker with scaphoid nonunion of the right wrist following an untreated scaphoid fracture (a); postoperative follow-up after adaptive proximal scaphoid implant implant placement and minimal styloidectomy, with anterior fiberglass splint still in place (b); 6-year follow-up (c); 17-year follow-up showing prosthetic notching against the proximal pole of the capitate (d); the patient declined further surgical intervention due to minimal pain and satisfactory function; clinical appearance at 17-year follow-up (e).

Discussion

This study presents long-term follow-up of the early cases of APSI implanted in our hospital. Follow-up assessment showed a satisfactory level of wrist function and a significant improvement compared with preoperative scores.

The primary goal of proximal scaphoid pole hemiarthroplasty is to provide replacement while preventing collapse of the proximal carpal row. Over time, various implants have been proposed for this purpose. Silicone prostheses were first introduced by Swanson; although long-term outcomes have been acceptable in terms of pain relief and functional recovery,^18,19 these implants were associated with high rates of secondary dislocation and significant bone resorption, likely due to synovitis induced by silicone debris. ²⁰ Other materials—including silastic, vitallium, ²¹ acrylic,^22,23 titanium, ²⁴ and ceramics—have also been explored, but none have demonstrated consistent clinical efficacy due to complications such as synovitis and high failure rates.^25,26 Experimental composite implants, such as those composed of glutaraldehyde-treated bovine fibrocartilage ²⁷ or collagen combined with bone morphogenetic protein, ²⁸ have similarly yielded unsatisfactory outcomes.

The APSI is composed of pyrocarbon, a biomechanically inert and biocompatible material with high resistance to abrasive wear and an elastic modulus closely matching that of cortical bone, thereby reducing the risk of stress shielding.^29-31

Reported complications associated with APSI implantation include palmar or dorsal dislocation, peri-implant osteolysis, improper implant sizing (which may result in radial styloid impingement or instability), persistent pain or limited ROM, and progression of joint degeneration. ⁸ As highlighted by Marcuzzi et al, ³² due to the lack of osteointegration with surrounding bone, the pyrocarbon implant develops a thin fibrous membrane around it. This layer likely provides partial protection of the scaphoid fossa. ⁷

Péquignot et al ¹¹ reported satisfactory functional outcomes following APSI implantation at a 6-year follow-up. These findings were subsequently confirmed by Grandis and Berzero ³³ in a retrospective study, which demonstrated favorable results in terms of pain relief, improved ROM, and strength. Santos et al ⁹ further validated the efficacy of the APSI implant at 6-year follow-up, reporting restoration of satisfactory wrist function without mechanical complications. Similarly, a prospective study by Daruwalla et al, ³⁴ with a mean follow-up of 18 months, demonstrated clinical and functional improvements. Finally, Ferrero et al ⁷ reported similar results with a mean follow-up of 5.6 years.

The results of our study are satisfactory in terms of carpal stability, reliability, and reproducibility of functional outcomes, including in long-term follow-up assessments. Regarding wrist function and patient satisfaction, our findings are consistent with those previously reported,^35-37 with a slightly greater improvement observed in the evaluated parameters. However, this may be partially attributable to higher preoperative ROM values in our cohort. Across all variables analyzed, preoperative and long-term postoperative values demonstrated statistically significant differences, confirming that the procedure led to objectively measurable clinical improvements sustained over time. Despite satisfactory functional recovery, about half of the patients required minor adaptations at work, mainly due to residual stiffness or discomfort, suggesting subtle limitations under high functional demands.

The use of the APSI for proximal scaphoid pole replacement appeared to decelerate the natural progression of osteoarthritis and carpal collapse. The absence of radiographic evidence of severe advanced osteoarthritic carpal degeneration suggests that the implant acts as a dynamic spacer, capable of adapting to wrist biomechanics while effectively replacing the damaged scaphoid proximal pole. However, a mild worsening of the osteoarthritic condition was qualitatively observed in 60% of patients, as evidenced by the appearance of osteophytes and a reduction in the joint space between the carpal bones. This result is slightly worse compared to that reported by Poumellec et al, ³⁶ likely attributable to the longer follow-up period. Moreover, many of the patients in our study were relatively young and presented with high functional demands. The absence of major deformities or mechanical complications further supports the validity of APSI as a therapeutic option for this patient population.

It is important to emphasize that improper sizing of the implant may lead to complications: Undersized implants can result in instability, whereas oversized implants may lead to overstuffing and associated pain with a risk of dislocation.

In no case was prosthesis removal required, and no instances of implant dislocation were observed. The only patient who reported recurrence of pain approximately 17 years after surgery was found to have an impingement between the scaphoid and an osteophyte on the radial styloid, previously treated with styloidectomy.

Nevertheless, the study presents several limitations, including the nonuniformity of follow-up duration, the relatively small sample size, the lack of quantitative monitoring of rehabilitation time and return to previously performed work duties, and potential bias introduced by all surgeries being performed by the same surgeon. Future studies would benefit from implementing serial evaluations with a standardized follow-up protocol. Furthermore, stratifying patients by age group may provide additional insights into the long-term efficacy of the APSI implant across different demographics, helping refine its indications and optimize patient outcomes.

Conclusion

The APSI pyrocarbon implant demonstrated reliable long-term clinical and radiographic outcomes in the treatment of proximal scaphoid nonunions and SNAC wrist, with sustained improvements in pain, strength, range of motion, and functional performance. Radiographic follow-up confirmed implant stability and suggested its role in delaying carpal collapse and advanced osteoarthritis. These findings support APSI as a viable, durable alternative in wrist-salvage procedures, particularly in young, high-demand patients.