DiscussionStress fractures due to overuse in young athletes have been widely described in various sports.7Caine D. DiFiori J. Maffulli N. Physeal injuries in children’s and youth sports: reasons for concern?. Specifically, among skeletally immature climbers, the dorsal aspect of the middle phalanx base is prone to epiphyseal fractures (Salter-Harris type III fractures).8Sport climbing from a medical point of view.,9Schöffl V. Popp D. Küpper T. Schöffl I. Injury trends in rock climbers: evaluation of a case series of 911 injuries between 2009 and 2012. These fractures are explained by an overuse of the “crimp grip position,” wherein the PIP joints are fully flexed and DIP joints are hyperextended. This results in high compressive forces on the dorsal aspect of the epiphysis and growth plate, which leads to the aforementioned fractures (Figure 3a).10Epiphyseal stress fractures in the fingers of adolescents: biomechanics, pathomechanism, and risk factors.

Figure 3A, The “crimp grip” position with the proximal interphalangeal joints fully flexed and distal interphalangeal joints hyperextended. B, The “open grip” position is the most extreme grip position. In this arrangement, the distal interphalangeal joint is flexed and the proximal interphalangeal joint is almost completely extended. At times, a climber’s entire body weight will be supported with the fingers in this position.

In contrast, the “open grip position,” wherein the DIP joint is flexed and the PIP joint is (nearly) fully extended (Figure 3b), leads to a different force distribution in the fingers. In this state, major tension forces are applied to the distal phalanx. A stress fracture occurs when repetitive tension stress exceeds the strength of the phalanx, causing a small part of the bone attached to a tendon or ligament to tear away from the central part of the bone.11Porr J. Lucaciu C. Birkett S. Avulsion fractures of the pelvis—a qualitative systematic review of the literature. Hence, when examining the case examples described here, relative to the distal phalanx, it is reasonable to conclude that a portion of the distal extensor digitorum communis tendon must attach to the proximal rim of the metaphysis of the distal phalanx.Although it has been previously described that the extensor digitorum communis tendons insert into the distal phalangeal epiphyses of their respective rays, our ultrasound examinations in children show an additional metaphyseal insertion of the extensor tendon (Figure 4).12Tendon and ligament attachments in relationship to growth plates in a child’s hand.

Figure 4Ultrasound image of the dorsal aspect of the right middle finger’s distal interphalangeal joint in a healthy 8-y-old child.

This configuration also aligns with the findings of Hoch et al,13Hoch J. Fritsch H. Lewejohann S. Plastination-histological investigations on the inserting extensor pollicis brevis tendon on the proximal phalanx of the thumb. who demonstrated through plastination histologic cross-sections of the fingers that a part of the extensor tendon indeed inserts into the proximal part of the diaphysis (Figure 5).14Frenz C. Fritsch H. Hoch J. Plastination histologic investigations on the inserting pars terminalis aponeurosis dorsalis of three-sectioned fingers. We believe that this anatomic configuration resembles that which is found in the ulnar and radial collateral ligaments that extend beyond the edge of the physis to integrate the periosteum of the distal phalanx, as detailed by Bogumill15A morphologic study of the relationship of collateral ligaments to growth plates in the digits. and verified via histologic sections.Figure 5Graphic representation of the quadruple insertion of the pars terminalis of the dorsal aponeurosis (extensor tendon). After Frenz et al.14Frenz C. Fritsch H. Hoch J. Plastination histologic investigations on the inserting pars terminalis aponeurosis dorsalis of three-sectioned fingers.The constellation of presenting symptoms and objective findings in the cases discussed herein represent a distinct type of injury. First, this fracture type appears to result from a highly specific overuse, namely, the “open grip position” in sport climbing. Second, this fracture type is specific to skeletally immature patients. Fusion of the epiphysis in the distal phalanges of the hand typically begins at the age of 12 y in girls and occurs between the ages of 13 and 17 y in boys.16Cardoso H.F.V. Severino R.S.S. The chronology of epiphyseal union in the hand and foot from dry bone observations. Consequently, in skeletally immature patients, the metaphyseal area is less stable and more susceptible to chronic stress and microfractures. The resulting metaphyseal fractures are analogous to Salter-Harris type II fractures. Third, this type of fracture pattern may be more likely to occur in males, like the cases presented herein, given the timing of physeal closure and the stability of the epiphysis, both of which are influenced by testosterone.4Bärtschi N. Scheibler A. Schweizer A. Symptomatic epiphyseal sprains and stress fractures of the finger phalanges in adolescent sport climbers.,6Hochholzer T. Schöffl V.R. Krause R. Finger-epiphysenverletzungen jugendlicher sportkletterer.

As mentioned previously, the specific type of fracture described herein is not commonly encountered in clinical practice. This rarity may be attributable to the unique biomechanical stresses inherent to sport climbing. Furthermore, individual differences in age and physiological variability may contribute to the development of this specific fracture type. Moreover, unless x-rays are obtained in a strict lateral view, this fracture type can be easily overlooked.

In both patients, a conservative treatment approach consisting of reduction in load-bearing activities of the finger and avoidance of terminal joint mobilization was successful. Therapeutic finger taping around the DIP joint prevents terminal joint flexion, specifically during return of activity.

Given that the “open grip” position explains the pathomechanics of this fracture type, we recommend a balanced training regimen in skeletally immature climbers (specifically those aged ≤18 y). The training should focus on increased volume and diversity of climbing routes rather than increased climbing intensity to help minimize the likelihood of injury and preserve the individuals’ climbing capabilities over the long term.

Future investigations on this topic should explore whether there is an optimal amount and duration of activity restriction needed following stress fractures of the distal phalanx. Moreover, studies should seek to quantify whether (and to what degree) the resumption of normal activity prior to full bone consolidation increases the relative risk for secondary complications, long-term sequalae, or other unfavorable outcomes.

Given the rapid growth in the popularity of both professional and recreational sport climbers, recognition of this unique presentation and fracture pattern is clinically meaningful for healthcare providers who are engaged in the treatment of young patients who present with climbing injuries. In doing so, clinicians will be able to accurately diagnose and manage this rare but important fracture type.

Author Contributions: study concept and design (ADW, AS); data acquisition (AS, ADW, LR); drafting and critical revision of the manuscript (ADW); approval of final manuscript (ADW, LR, AS).

Financial/Material Support: None.

Disclosures: ADW reports support from Balgrist University Hospital for any publication or related fees associated with this study and a working contract or agreement with Balgrist University Hospital and University Children’s Hospital of Zurich.