Anatomy of the Lumbrical Muscles: Implications for Mechanical Advantage.

BACKGROUND: The lumbrical muscles comprise 4 intrinsic muscles of the hand and are involved in flexion of the metacarpophalangeal joint (MCPJ) and extension of the proximal interphalangeal and distal interphalangeal joints. The purpose of this study was to investigate the anatomical mechanics of the lumbrical muscles of the index, middle, ring, and small fingers. METHODS: We evaluated 25 cadaver arms and measured the distance between the MCPJ and fingertip, the distance between the MCPJ and lumbrical muscle insertion, and the distance between the MCPJ and the most proximal lumbrical muscle origin. With these measurements we calculated the needed force, insertion ratio (length of the proximal, middle, and distal phalanx divided by the MCPJ to insertion distance), and lumbrical muscle length. RESULTS: We found that the force was significantly different between all fingers, except for the comparison of the index and ring finger (P = .34). In addition, we found that muscle length was significantly different between most the fingers, except for the comparison between the index and middle fingers (P = .24), and index and ring fingers (P = .20). There was no significant difference in insertion ratio. CONCLUSIONS: Our study suggests that the anatomical mechanics for the motor function of the lumbrical muscles are similar in all fingers. This could further imply that movements are equally precise in all fingers resulting in coordination with one another and, therefore, adequate hand function. LEVEL OF EVIDENCE: IV.

Clinical outcomes after primary repair for thumb ulnar collateral ligament ruptures: a systematic review and meta-analysis.

There is no consensus on the best surgical technique for treating thumb ulnar collateral ligament (UCL) ruptures. This systematic review and meta-analysis investigates which primary repair technique and postoperative immobilization protocol result in the best clinical outcomes. A literature search was conducted in Embase, Medline ALL Ovid, Web of Science Core Selection and Cochrane Central Register of Controlled Trials. Pain, stability, tip pinch strength, key pinch strength, grip strength, return to work and metacarpophalangeal joint range of motion were collected as postoperative outcomes. In total, 29 studies were included. All surgical techniques resulted in satisfactory clinical outcomes, with no significant differences between bone anchor reinsertion, suture fixation, K-wire fixation and a combination of techniques. K-wire immobilization resulted in worse postoperative pain, but similar stability compared to immobilization without a K-wire. Clinical outcomes after thumb UCL repair are excellent, with no differences in clinical outcomes noted among surgical techniques.

Complications and Unplanned Reoperation After Thumb Metacarpophalangeal Arthrodesis.

PURPOSE: Arthrodesis of the metacarpophalangeal (MCP) joint of the thumb is a common procedure to treat arthritis or instability. Studies reporting hardware complications and nonunion rates after thumb MCP joint arthrodesis report on small sample sizes. We aimed to describe the hardware complication rate, the nonunion rate, and the number of thumbs that achieve union among patients undergoing thumb MCP joint arthrodesis. METHODS: A database spanning 5 urban hospitals in a single metropolitan region in the United States was searched for patients who underwent thumb MCP joint arthrodesis between January 1, 2004 and January 1, 2020. After reviewing patient records, we identified 122 thumbs that underwent MCP joint arthrodesis and had a minimum follow-up of 90 days. The primary outcome was unplanned reoperation after hardware complications and nonunion. Second, the number of thumbs that achieved radiographic union was reported for the tension band and screw fixation arthrodesis group. RESULTS: Twenty-two (18%) out of 122 thumbs had hardware complications after thumb MCP joint arthrodesis, and 11 (9%) out of 122 thumbs developed a nonunion. Patients who underwent screw fixation arthrodesis had no events of hardware complications and subsequent hardware removal. The nonunion rate was 9/65 (14%) in the tension band arthrodesis group and 2 (4%) of 45 in the screw fixation arthrodesis group. Of the thumbs that had available radiographs to assess the healing of the arthrodesis, 34 (81%) of 42 were radiographically united in the tension band arthrodesis group and 29 (91%) of 32 in the screw fixation group. CONCLUSIONS: Our data suggest that screw fixation has fewer hardware complications and a lower reoperation rate than tension band arthrodesis. TYPE OF STUDY/LEVEL OF EVIDENCE: Prognosis IV.

Patient-Reported Outcomes and Function After Surgical Repair of the Ulnar Collateral Ligament of the Thumb.

PURPOSE: The purpose of this study was to report prospectively collected patient-reported outcomes of patients who underwent open thumb ulnar collateral ligament (UCL) repair and to find risk factors associated with poor patient-reported outcomes. METHODS: Patients undergoing open surgical repair for a complete thumb UCL rupture were included between December 2011 and February 2021. Michigan Hand Outcomes Questionnaire (MHQ) total scores at baseline were compared to MHQ total scores at three and 12 months after surgery. Associations between the 12-month MHQ total score and several variables (i.e., sex, injury to surgery time, K-wire immobilization) were analyzed. RESULTS: Seventy-six patients were included. From baseline to three and 12 months after surgery, patients improved significantly with a mean MHQ total score of 65 (standard deviation [SD] 15) to 78 (SD 14) and 87 (SD 12), respectively. We did not find any differences in outcomes between patients who underwent surgery in the acute (<3 weeks) setting compared to a delayed setting (<6 months). CONCLUSIONS: We found that patient-reported outcomes improve significantly at three and 12 months after open surgical repair of the thumb UCL compared to baseline. We did not find an association between injury to surgery time and lower MHQ total scores. This suggests that acute repair for full-thickness UCL tears might not always be necessary. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic II.