Helping Surgeons' Hands: A Biomechanical Evaluation of Ergonomic Instruments

PURPOSE

"Ergonomic" is a common descriptor for a desk or computer workspace but is a term rarely used to describe a surgical instrument. Instead, surgeons spend many hours in inconvenient positions, often using instruments that are not ergonomic. Improving the ergonomics of surgical instruments may decrease the required force for simple tasks and allow for more efficient surgery.

METHODS

To evaluate the impact of ergonomic surgical instruments, the authors developed ergonomic screwdriver handles. The shape and size of these handles were engineered using previous dental studies and 3-dimensional modeling to create an ideal handle for specific glove sizes. Participants were recruited to test 3 different ergonomic handle sizes against a standard screwdriver while assessing digital peak force, digital contact area, and participant preference. Ten participants (3 women) with glove sizes ranging from 6 to 8 were evaluated.

RESULTS

Ergonomic screwdriver handles sized for glove sizes 6 and 7 required significantly less thumb peak force than the standard screwdriver for all participants (702 N for glove size 6 and 567 N for glove size 7 ergonomic screwdrivers, vs 1780 N for "one size fits all" standard screwdriver). Participants consistently preferred screwdrivers that required lower thumb and index finger forces. All ergonomic handles required lower thumb and index finger force. Eighty percent of participants preferred a screwdriver modeled within 1 glove size of their own.

CONCLUSIONS

Improved ergonomic handles require less force and are preferred by surgeons.

CLINICAL RELEVANCE

The significant decrease in thumb peak force for glove sizes 6 and 7 suggests that there is room for ergonomic improvement in instruments, especially for surgeons with smaller hands. Manufacturing ergonomic screwdriver handles and using the evolving convenience of 3-dimensional printing may help to develop a more comfortable work environment for surgeons.

Threaded Intramedullary Nails Are Biomechanically Superior to Crossed K-wires for Metacarpal Neck Fractures

BACKGROUND

Intramedullary nail (IMN) fixation of metacarpal fractures is an alternative to Kirschner wire (K-wire) fixation. The goal of this study was to compare the biomechanical properties of K-wire fixation with a threaded IMN (InNate; ExsoMed, Aliso Viejo, California).

METHODS

The study design was based on previously described biomechanical models for evaluating metacarpal fractures. Sixteen fresh frozen small finger-matched and ring finger-matched pairs were randomized to either IMN or 0.045 in K-wire fixation after receiving a standardized neck osteotomy. Proper implant placement was confirmed with plain radiographs. Specimens then underwent loading in a 3-point bend configuration. Load to failure (LTF), stiffness, and fracture displacement were recorded. Mechanical failure was defined by a sharp change in the load-displacement curve.

RESULTS

Age, sex, sidedness (left or right), and digit (ring or small finger) were evenly distributed between groups. The IMN had a significantly higher LTF than K-wires (546 N vs 154 N, P < .001). The K-wire fixation demonstrated plastic deformation between 75 and 150 N. Intramedullary nail stiffness was higher than that of K-wires (155.89 N/mm vs 59.28 N/mm, P < .001).

CONCLUSIONS

When surgical fixation is indicated for metacarpal neck and shaft fractures, the threaded IMN is biomechanically superior to crossed K-wires with the application of 3-point bend.

Concurrent Ring Finger Middle Phalanx Fracture and Jersey Finger in a Rugby Player

Avulsions of the flexor digitorum profundus (FDP) tendon and phalanx fractures are both common injuries for rugby players, but these concurrent injuries in the same finger have not been previously described. This case describes a 20-year-old female rugby player who sustained a right ring finger comminuted, mildly displaced middle phalanx fracture. The patient was evaluated by a hand surgeon 3 weeks after the injury, and non-operative management with a splint was elected. One week later, upon further examination, the patient demonstrated persistent inability to flex the distal interphalangeal joint (DIPJ) of the ring finger. Ultrasound was inconclusive but an MRI demonstrated avulsion of the FDP tendon from the distal phalanx, consistent with a jersey finger injury. The patient subsequently underwent open repair of the FDP tendon. This case illustrates the importance of careful physical exam and index of suspicion for coexisting injuries.

Irreducible Volar DRUJ Dislocation with Distal Radius Fracture Dislocation

Background  Volar dislocations of the distal radioulnar joint (DRUJ) are rare and often missed during initial evaluation. Chronic dislocations and disability can occur when DRUJ dislocations are unrecognized and not reduced. DRUJ dislocations often occur with other wrist injuries, which may complicate reduction. Closed reduction can fail to reduce DRUJ dislocations, in which case open reduction is necessary. Case Description  This case describes a patient who had a volar dislocation of the DRUJ with an associated dorsal distal radius fracture dislocation. Initial attempts at closed reduction were unsuccessful which prompted surgical intervention. After open reduction and internal fixation of the distal radius fracture dislocation, closed reduction of the DRUJ remained unsuccessful. This prompted an open reduction of the DRUJ. Surgical exposure demonstrated that the extensor carpi ulnaris and the distal radius had prevented closed reduction of the DRUJ. Postoperatively, a splint was placed with the wrist in supination. The patient followed-up at the 2- and 4-month intervals with persistent subluxation. However, the patient also reported minimal pain and the ability to return to work and previous level of activity. Literature Review  Current literature regarding irreducible volar DRUJ dislocations with distal radius fracture dislocations includes sparse case reports, which are reviewed in this report. Clinical Relevance  This case illustrates successful treatment for an uncommon volar DRUJ dislocation associated with a dorsal distal radius fracture dislocation and can be utilized to help guide future treatment of similar complex cases.

Early post-operative outcomes of plate versus nail fixation for humeral shaft fractures

INTRODUCTION

This study was designed to measure early postoperative outcomes of plate vs. nail fixation for humeral shaft fractures.

PATIENTS AND METHODS

Patients ≥18 years who underwent plate or nail fixation for low-energy humeral shaft fractures between 2005-2016 were identified from the National Surgical Quality Improvement Program (NSQIP). Multivariable regression was used to compare postoperative outcomes using propensity score adjustment to account for differences between fixation groups. Variables included in the propensity score were age, American Society of Anesthesiologists (ASA) class, hypertension, steroid use, cancer, functional status, chronic obstructive pulmonary disease (COPD), congestive heart failure (CHF), and sex.

RESULTS

Plate fixation was used in 1418 patients (70.6%), while nail fixation was used in 591 (29.4%). Patients undergoing nail fixation were more likely to be older, have a higher American Society of Anesthesiologists (ASA) class, and have comorbidities. Mean operative time was statistically longer in the plate fixation group (130 +/-62 min vs. 102 +/-54 min). After propensity score adjustment, type of fixation was not a significant predictor of major or minor complications, length of stay, or readmission. However, nail fixation was a significant predictor of mortality following propensity score adjustment (OR 3.15, 95% Confidence interval 1.26-7.85).

CONCLUSION

Patients undergoing intramedullary nail fixation tended to be older patients with more comorbidities, suggesting that surgeons are selecting nail fixation in patients who may not be ideal surgical candidates. Although LOS, complications, and readmission rates were higher in the nail group, this difference was not statistically significant following propensity score adjustment. However, nail fixation remained an independent predictor of 30-day mortality following adjustment. This suggests that nail fixation may not be a safer surgical option in patients with multiple medical co-morbidities and low-energy humeral shaft fractures.

Biomechanical Comparison of Flexor Digitorum Profundus Avulsion Repair

Purpose  Multiple repair techniques have been investigated for flexor digitorum profundus (FDP) tendon avulsions. The purpose of this study is to compare the biomechanical characteristics of a new fully threaded titanium suture anchor with previously examined fixation techniques. Methods  Repair of FDP tendon avulsions was performed in 18 fresh-frozen cadavers using one of three implants: Nano Corkscrew FT 1.7 mm suture anchor (Group 1; Arthrex, Inc., Naples, FL; n  = 6), Mitek Micro 1.3 mm suture anchor (Group 2; Mitek Surgical Products, Westwood, MA; n  = 6), or pullout suture button fixation (Group 3; n  = 6). Constructs were preloaded before testing load to failure. For each trial, elongation at 20 N and maximum load, mean load to failure, stiffness, and failure mechanism were recorded. Results  Load to failure occurred in all trials. Mean load to failure was significantly greater for Group 1 (61.6 ± 18.9 N) compared to Group 2 (42.5 ± 4.2 N; p  < 0.05) and Group 3 (41.6 N ± 8.0 N; p  < 0.05). Stiffness was significantly greater in Groups 1 and 2 compared to Group 3 (6.9 ± 2.2 N/mm vs. 6.1 ± 0.8 N/mm vs. 3.1 N/mm ± 0.5 N/mm, respectively, p  < 0.01). Mechanism of failure differed between the groups: Group 1 broke at the anchor in two trials and tore through the tendon in three trials, Group 2's suture universally broke at the anchor, and Group 3's trials mainly failed at the button. Conclusions  The Nano Corkscrew anchor (Group 1) has a significantly higher load to failure when compared with the other techniques. The higher load to failure of the corkscrew anchor provides a secure method for flexor tendon repair in zone I. Clinical Relevance  A fully threaded titanium suture anchor used for FDP tendon avulsion injuries is likely to withstand early active range of motion protocols.

Plate Fixation With Cancellous Graft for Scaphoid Nonunion With Avascular Necrosis

PURPOSE

Currently, there is no consensus on the optimal treatment for scaphoid nonunion with avascular necrosis (AVN). Various techniques, often involving vascularized corticocancellous bone grafting, have been proposed. The authors hypothesized that similar outcomes might be possible with volar plate fixation augmented with autogenous pure cancellous graft.

METHODS

The authors performed a retrospective chart review of 13 cases of scaphoid nonunions with AVN in 12 patients treated with plate fixation and pure cancellous bone grafting. Surgical management included a volar incision, reduction, impaction of cancellous bone graft from the ipsilateral olecranon and/or distal radius, and application of a volar locking plate. Postoperative outcome measures included time to union based on computed tomography, patient-reported pain and disability scores, grip strength, range of motion, and return to work and sports.

RESULTS

The average patient was 32 years old (range, 17-50 years) and treated an average of 18 months after initial injury (range, 6-49 months). Two of 12 patients (15.7%) were female, 3 of 12 patients (25%) were smokers, and 5 of 12 patients (41.7%) had failed union with previous screw fixation. Twelve scaphoids (92.3%) were treated for AVN associated with a proximal pole fracture, and 1 (7.7%) for AVN proximal to a scaphoid waist fracture. Mean follow-up was 19.5 months (range, 12-29 months). Union was achieved in all patients. Two scaphoids (15%) achieved union by 12 weeks, 7 scaphoids (54%) by 18 weeks, 2 scaphoids (15%) by 24 weeks, and 2 scaphoids (15%) by 30 weeks (range, 8.9-28 weeks). Mean Disabilities of the Arm, Shoulder, and Hand score improved from 30.6 ± 6.2 before surgery to 17.2 ± 6.5 after surgery. All 11 employed patients returned to work, although 3 (27.2%) did not return to full capacity.

CONCLUSIONS

Scaphoid plate fixation and pure nonvascularized cancellous bone grafting for scaphoid nonunion with AVN yields excellent union rates and good patient-reported and functional outcomes.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Outcomes of Unstable Scaphoid Nonunion With Segmental Defect Treated With Plate Fixation and Autogenous Cancellous Graft

PURPOSE

Treatment of scaphoid nonunion with a segmental defect presents a challenging clinical problem. Various techniques have been proposed, often involving structural grafting with vascularized and nonvascularized bone. The authors hypothesize that satisfactory clinical and radiographic outcomes are possible with a relatively simplified technique of volar plate fixation with autogenous, purely cancellous graft.

METHODS

The authors performed a retrospective review of 34 patients with scaphoid nonunions with segmental defects, treated with plate fixation and purely cancellous bone grafting. Cases with avascular necrosis were excluded. Surgical management included a volar incision, reduction, bone grafting from the ipsilateral distal radius and/or olecranon, and application of a volar locking plate. Postoperative outcome measures included time to union based on computed tomography, return to work and sports, patient-reported pain and disability scores, grip strength, and range of motion.

RESULTS

Thirty-four patients with an average age of 31 years (range, 16-55 years) were treated with volar plate fixation and cancellous grafting, an average of 34 months after initial injury. Twenty-six patients (76%) were treated for nonunion at the scaphoid waist, 7 (21%) at the proximal pole, and 1 (3%) at the distal pole. Mean final follow-up was 18.7 months (range, 12-34 months). When union was defined by computed tomography evidence of healing, 2 (6%) scaphoids healed by 6 weeks after surgery, 28 (82%) healed by 12 weeks, and 100% healed by 18 weeks. Mean Disabilities of the Arm, Shoulder, and Hand score improved from 27.1 ± 7.3 before surgery to 11.8 ± 5.8 after surgery. Grip strength, corrected for hand dominance, improved from 77.5% of the nonsurgical side before surgery to 90.5% after surgery. All employed patients returned to work, although 3 (9%) did not return to full capacity.

CONCLUSIONS

The combination of scaphoid plate fixation and pure cancellous bone grafting for scaphoid nonunion with segmental defects yields reliable union rates and good patient outcomes. Autogenous cancellous grafting may be an alternative to more technically demanding or morbid grafting procedures for the treatment of scaphoid nonunion.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Does Greater Trochanter Decortication Affect Suture Anchor Pullout Strength in Abductor Tendon Repairs? A Biomechanical Study

BACKGROUND

Greater trochanter decortication is frequently performed at the time of abductor tendon repair to theoretically increase healing potential. No previous studies have determined the effect that greater trochanter decortication has on the pullout strength of suture anchors. Hypothesis/Purpose: The purpose of this study is to determine whether greater trochanter decortication and bone mineral density affect suture anchor pullout strength in abductor tendon repair. The authors hypothesize that both will have a significant detrimental effect on suture anchor pullout strength.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nineteen cadaveric proximal femurs with accompanying demographic data and computed tomography scans were skeletonized to expose the greater trochanter. Bone density measurements were acquired by converting Hounsfield units to T-score, based on a standardized volumetric sample in the intertrochanteric region of the femur. The gluteus medius insertion site on the lateral facet of the greater trochanter was evenly divided into 2 regions, anterior-distal and posterior-proximal, and each region was randomly assigned to receive either no decortication or 2 mm of bone decortication. A single biocomposite anchor was implanted in each region and initially tested with cyclic loading for 10 cycles at 0-50 N, 0-100 N, 0-150 N, and 0-200 N, followed by load to failure (LTF) tested at 1 mm/s. For each trial, the number of cycles endured, LTF, mechanism of failure, and stiffness were recorded.

RESULTS

Greater trochanters with no decortication and 2 mm of decortication survived a mean ± SD 35.1 ± 6.4 and 28.5 ± 10.6 cycles, respectively ( P < .01). Load to failure for nondecorticated specimens was 206.7 ± 75.0 N versus 152.3 ± 60.2 N for decorticated specimens ( P < .001). In a multivariate analysis, decortication and bone density were determinants in LTF ( P < .05).

CONCLUSION

Decortication and decreased bone mineral density significantly decreased the pullout strength of suture anchors in the lateral facet of the greater trochanter.

CLINICAL RELEVANCE

Bone density should be considered when determining whether to perform greater trochanter decortication in abductor tendon repairs.