Orthopedics

Feature Article 

Identifying the Safe Zone in Arthroscopic Anterior Elbow Capsulectomy: A Cadaveric Study

Kenneth M. Chin, MD; Mohit N. Gilotra, MD; Steven Horton, MD; S. Ashfaq Hasan, MD

Abstract

The authors assessed the effects of forearm rotation on the proximity of the radial nerve and medial collateral ligament (MCL) to a proximal and a more distal arthroscopic anterior elbow capsulectomy. Arthroscopy was performed on 10 cadaveric specimens. Sutures were passed lateral to medial at the level of the radiocapitellar joint and at the proximal edge of the annular ligament. Dissection measured the distance to the radial nerve from the lateral starting point and to the MCL from the medial exit point in varying degrees of forearm rotation. The extent of brachialis muscle coverage of the radial nerve was documented. The distance from the starting point to the radial nerve increased in pronation at both levels. The medial extent of the capsulectomy remained a safe distance from the MCL. Brachialis muscle covered the radial nerve at both levels. Pronation increases the capsulectomy safe zone, including more distally, before encountering the radial nerve; the MCL is not at risk. [Orthopedics. 2020;43(5):e399–e403.]

Abstract

The authors assessed the effects of forearm rotation on the proximity of the radial nerve and medial collateral ligament (MCL) to a proximal and a more distal arthroscopic anterior elbow capsulectomy. Arthroscopy was performed on 10 cadaveric specimens. Sutures were passed lateral to medial at the level of the radiocapitellar joint and at the proximal edge of the annular ligament. Dissection measured the distance to the radial nerve from the lateral starting point and to the MCL from the medial exit point in varying degrees of forearm rotation. The extent of brachialis muscle coverage of the radial nerve was documented. The distance from the starting point to the radial nerve increased in pronation at both levels. The medial extent of the capsulectomy remained a safe distance from the MCL. Brachialis muscle covered the radial nerve at both levels. Pronation increases the capsulectomy safe zone, including more distally, before encountering the radial nerve; the MCL is not at risk. [Orthopedics. 2020;43(5):e399–e403.]

The stiff elbow is a challenging problem for orthopedists. Arthrofibrosis of the elbow can result from several causes, including trauma, osteoarthritis, prolonged immobilization, rheumatoid arthritis, burns, traumatic brain injury, and congenital conditions. Treatment of these lesions typically starts with conservative measures but can require operative intervention. Traditionally, open approaches were used to tackle elbow contractures. The open method often involved extensive dissection, sometimes requiring multiple exposures, which can increase the risk of complications, such as bleeding, heterotopic ossification, iatrogenic instability, wound complications, recurrence of stiffness, and marked pain.1–8

Elbow arthroscopy has become more versatile with the advancement of instrumentation and the comfort level of surgeons. The arthroscopic anterior elbow capsulectomy was first described in the early 1990s.9 Several case series have shown improvement in elbow arc of motion with this minimally invasive procedure.9–11 Although results are promising, this procedure remains technically demanding and elbow arthroscopy has a steep learning curve.

Case reports of iatrogenic radial nerve injuries during arthroscopic capsulectomy have been published, and these injuries might be under-reported complications.9,12,13 Considering the vulnerability of the radial nerve during arthroscopic anterior capsulectomy, strategies have been developed to minimize risk to the nerve, including stripping and elevating the anterior capsule from the humerus proximally, using arthroscopic retractors, and initiating the capsulotomy proximally.14 Savoie and Jones15 described performing the initial capsulotomy at the level of the coronoid fossa. Further capsulectomy can then be performed from proximal to distal. A more extensive capsulectomy might help in increasing postoperative range of motion. However, the extent of the distal capsulectomy is limited by concerns regarding potential neurovascular injury, especially laterally, with most recommendations being to stop at the level of the radiocapitellar joint to minimize the risk of radial nerve injury. The current authors believe a more distal, alternative capsulectomy can be safely undertaken at the level of the proximal edge of the annular ligament and can include the radial capsule.

Omid et al16 performed a cadaveric study describing the anatomy of the radial nerve in relation to the anterior capsule. They were able to estimate a mean safe zone of 20 mm at the level of the radiocapitellar joint between the starting point of a capsulectomy laterally and the point at which the radial nerve crossed the capsule.16 However, previous studies have not investigated the effect of forearm rotation on the safe zone of an arthroscopic anterior capsulectomy in relation to the radial nerve. The relation of the radial nerve to an insufflated capsule might not change with forearm rotation. In addition, no studies have evaluated the proximity of the medial collateral ligament (MCL) to the medial extent of the anterior capsulectomy.

The first aim of this study was to assess the effect of varying forearm rotations on the distance from the radial nerve and MCL to the starting and exiting points, respectively, of a simulated arthroscopic anterior capsulectomy using a cadaveric joint insufflated model. This was done for the more commonly used capsulectomy starting point at the level of the radiocapitellar joint and for an alternate, more distal, starting point for the capsulectomy at the level of the proximal annular ligament. For the second aim, and considering conflicting reports in the current literature, the authors wanted to observe whether the brachialis muscle belly is reliably interposed between the capsule and radial nerve over a proposed anterior capsulectomy.

Omid et al16 documented that brachialis coverage was lost at the level of the radial neck in 55% of specimens, leaving the nerve exposed just adjacent to the anterior distal capsule. This is in contrast to the study by Thoreux et al,17 which reported the radial nerve being covered by the brachialis over the course of an anterior capsulectomy.

The current authors' hypothesis was that by using a cadaveric simulation with elbow joint insufflation, a safe zone and a safe position for arthroscopic anterior elbow capsular release could be identified.

Materials and Methods

Ten fresh-frozen cadaveric upper-extremity specimens spanning from the disarticulated glenohumeral joint to the hand were obtained from the Department of Anatomy at the authors' institution. None of the specimens used in the study had evidence of previous surgery or injury to the elbow. No evidence of notable osteoarthritis or appreciated capsular contracture was present in any elbow studied. Mean age of the cadavers was 82 years. Six specimens were male and 4 were female. Five specimens were right sided and 5 were left sided.

The first phase of the study entailed transfixing the elbow with a 2.5-mm Steinmann pin across the ulnohumeral joint in 90° of flexion and mounting the specimen in a clamp, simulating patient positioning for arthroscopy. The elbow joint was then insufflated with 15 to 25 mL of normal saline solution at the lateral “soft spot” between the capitellum, radial head, and olecranon until slight resistance was felt. An arthroscopy was then performed through a standard anteromedial portal (no lateral portals were made). The portal was placed 1.5 cm anterior and 2 cm proximal to the medial epicondyle. The elbow was insufflated with gravity-dependent saline.

Once the radiocapitellar joint line was visualized through the anteromedial viewing portal, a beath pin was placed laterally, entering the joint at the most lateral edge of the radiocapitellar joint space that could be visualized and exiting straight across medially. A suture (S1) was placed through the pin and into the joint for reference during dissection. The suture was secured outside the elbow with a clamp to prevent migration during dissection. The suture represents the distal limit of a standard capsulectomy.

The beath pin was again introduced, this time distally at the level of the annular ligament. The pin was passed straight across the joint from as far lateral as possible, exiting medially, allowing placement of a second suture (S2), which was secured outside the elbow joint (Figure 1). The second suture represented the distal aspect of an alternate capsulectomy to remove the distal radial capsule. The entry and exit points of S1 and S2 represent the most lateral and most medial points, respectively, of the capsulectomy.

Lateral anatomy of the elbow shows suture 1 (S1) (traditional distal extent of capsulectomy) and suture 2 (S2) (alternative distal extent of capsulectomy).

Figure 1:

Lateral anatomy of the elbow shows suture 1 (S1) (traditional distal extent of capsulectomy) and suture 2 (S2) (alternative distal extent of capsulectomy).

The second phase was open anatomic dissections. The elbow was kept at 90° of flexion, as previously transfixed. Before dissection, the joint was reinsufflated with 15 to 20 mL of a normal saline solution to better define the capsule and to simulate arthroscopic conditions. The skin and subcutaneous fat were dissected from the specimens, exposing the underlying brachial and antebrachial fascia. Dissection was carefully performed over the interval corresponding to the brachialis and brachioradialis by identifying the brachioradialis in the forearm and working proximally. The radial nerve was identified between the brachialis and brachioradialis, and stay stitches were placed in the nerve where it lay into the surrounding soft tissue.

The distance from the radial nerve to the previously placed sutures (S1 and S2) at the lateral capsule locations was measured in 3 positions of rotation: neutral, full pronation, and full supination. In addition, the presence or absence of coverage of the radial nerve by the brachialis muscle was noted for each dissection (Figure 2).

Photograph of gross dissection of the lateral elbow shows the proximity of suture 1 (S1) and suture 2 (S2) to the radial nerve (n).

Figure 2:

Photograph of gross dissection of the lateral elbow shows the proximity of suture 1 (S1) and suture 2 (S2) to the radial nerve (n).

A medial approach was then used to identify the MCL and to expose the anteromedial capsule. Measurements were obtained from the suture exit point (S1 and S2) in the medial capsule to the MCL in all 3 positions of forearm rotation (Figure 3).

Photograph of gross dissection of the medial elbow shows the proximity of suture 1 (S1) and suture 2 (S2) to the medial collateral ligament (MCL).

Figure 3:

Photograph of gross dissection of the medial elbow shows the proximity of suture 1 (S1) and suture 2 (S2) to the medial collateral ligament (MCL).

All arthroscopic and open dissections were performed in a standardized fashion. Measurements were obtained using a handheld sliding digital caliper (General Tools & Instruments, New York, New York) calibrated to 0.01 mm, with all measurements were performed by a single observer (S.H.).

Mean, minimum, maximum, and standard deviations were calculated for each measured value. Two-tailed paired t tests were used to compare measured values regarding elbow positioning and distances.

Results

The distances from the starting point of the simulated anterolateral capsulectomy to the radial nerve at both S1 (conventional) and S2 (alternative) varied based on the position of forearm rotation (Table 1). In neutral rotation, mean distances were 18.8 and 14.8 mm at S1 and S2, respectively. In supination, the nerve was a mean of 17.3 mm (±5.95 mm; 95% confidence interval [CI], 13.6–21.0 mm) from the starting point of the capsulectomy at S1 and 13.6 mm (±5.80 mm; 95 CI, 10.0–17.2 mm) distally at S2. Pronated, the distance was a mean of 19.6 mm (±6.14 mm; 95% CI, 15.8–23.4 mm) proximally and 16.1 mm (±5.81 mm; 95% CI, 12.5–19.7 mm) distally.

Distance From Anterolateral Capsular Suture to Radial Nerve

Table 1:

Distance From Anterolateral Capsular Suture to Radial Nerve

The increase in the distance between full supination and full pronation was statistically significant at both S1 (2.3 mm; P<.01) and S2 (2.5 mm; P<.01), with the nerve moving away from the lateral starting point in pronation compared with supination. When comparing neutral rotation with supination, the latter increased the safe zone before the nerve crossed the capsulectomy with a mean difference of 1.46 mm (P=.03) at the proximal capsule and 1.24 mm distally (P=.07; Table 2). In all dissected specimens, the radial nerve was covered by the brachialis muscle belly at both S1 and S2.

Change in Radial Nerve Distance to Capsule During Forearm Rotation

Table 2:

Change in Radial Nerve Distance to Capsule During Forearm Rotation

With the forearm in neutral rotation, the distance from the MCL to the exit point of the capsulotomy was found to be a mean of 12.9 mm (±2.63 mm; 95% CI, 10.2–15.5 mm) at S1 and 13.8 mm (±4.12 mm; 95% CI, 9.7–18.0 mm) at S2. When pronated, the MCL to exit distance was approximately 13.3 mm (±2.81 mm; 95% CI, 10.5–16.1 mm) at S1 and 13.3 mm (±0.77 mm; 95% CI, 9.5–17.0 mm) at S2. With the elbow supinated, the MCL to exit point distance was estimated to be 13.4 mm (±2.99 mm; 95% CI, 10.4–16.4 mm) at S1 and 13.5 mm (±3.93 mm; 95% CI, 9.6–17.4 mm) at S2 (Table 3).

Distance From Medial Capsular Suture to Medial Collateral Ligament

Table 3:

Distance From Medial Capsular Suture to Medial Collateral Ligament

The changes in distance of the S1 and S2 markers in the capsule to the MCL during rotation of the forearm varied slightly with means from 0.14 mm (P=.74) proximally and 0.55 mm (P=.14) distally (Table 4). These data show at least a 1-cm interval between the exiting point of the anterior capsulectomy and the MCL.

Change in MCL Distance to Capsule During Forearm Rotation

Table 4:

Change in MCL Distance to Capsule During Forearm Rotation

Discussion

Elbow arthroscopy continues to be an evolving tool in the field of orthopedics. Indications have expanded for its use, including anterior capsulectomy for the arthrofibrotic elbow. This procedure has some advantages over open capsulectomy, such as decreased soft tissue dissection and postoperative pain, minimal incision size, diminished blood loss, and potentially shorter operative times.18 However, arthroscopic capsulectomy is technically demanding and is associated with a risk of iatrogenic nerve injury.12,19,20 The structure that is most at risk during this procedure is the radial nerve anterolaterally. Several case studies have reported radial nerve injuries during anterior elbow arthroscopy.12,19,20 Other structures, such as the ulnar and median nerves, are less at risk. To the current authors' knowledge, whether the MCL is at risk medially during an arthroscopic anterior capsulectomy has not been studied.

The current authors' first aim was to show the effect of varying forearm rotations on the distance from the radial nerve and MCL from the lateral starting point of a simulated arthroscopic anterior capsulectomy. They designed the study to evaluate this at both a conventional (S1) and an alternative, more distal (S2), capsulectomy. At both S1 and S2, forearm pronation provided increased distance to the radial nerve from the lateral starting point of the capsulectomy compared with neutral rotation. Comparing pronation with supination resulted in a further increase in the protective distance (2.28 and 2.48 mm, respectively). Although this does not seem to represent a large absolute increase, it is arguably clinically relevant because the simple act of pronation increases the safe zone for a laterally based arthroscopic capsulectomy and might help avoid iatrogenic radial nerve injury. Most arthroscopic biters measure approximately 3 mm, so this protective effect with pronation is potentially clinically relevant.

The current authors discovered that a more distal capsulectomy could safely be performed compared with a traditional, more proximal level. When a more distal capsulectomy was performed at S2, a safe interval was still present between the lateral starting point and the radial nerve, at 16.1 mm with pronation.

On the medial side of the elbow, no significant changes were observed in the distance from S1 and S2 to the MCL regarding forearm rotation (Table 4). This is likely because the MCL is an anatomic structure that is more intimately related with the capsule compared with the radial nerve. Forearm rotation also acts about the radial head within the sigmoid notch laterally, much farther away from the MCL. The MCL was not violated by the medial extent of the capsulectomy, with minimum distances of 8.6 mm (range, 8.6–18.3 mm) and 7.2 mm (range, 7.2–19.5 mm) found at S1 and S2, respectively. Therefore, the MCL can be considered to be at minimal risk with the proposed capsulectomy. To the current authors' knowledge, the anatomic relationship of the MCL to an anterior capsulectomy has not been previously studied.

The authors' second aim was to evaluate the brachialis muscle and its protection of and relation to the radial nerve at the level of the elbow capsule. Previous studies have shown the importance of the brachialis muscle in protecting the radial nerve during an arthroscopic anterior capsulectomy. In the current study, all specimens had the radial nerve protected by the brachialis at the proposed capsulectomy level. This is consistent with a cadaveric study performed by Thoreux et al,17 who also found brachialis coverage of the radial nerve in all of their specimens anterolaterally, both at the level of the radiocapitellar joint and at the radial neck. However, this is in contrast to the cadaveric study by Omid et al,16 who reported that only 45% of specimens had brachialis coverage of the radial nerve at the distal anterolateral capsule at the level of the radial neck. The disparity is likely because of a more proximal reference point in the current study, which was at the level of the proximal aspect of the annular ligament.

To the authors' knowledge, this is the first study that evaluates the relationship of the radial nerve and MCL to an arthroscopic anterior capsulectomy regarding forearm rotation. This evaluation is the primary strength of this research, which shows that simply pronating the forearm will likely have a protective effect on the position of the radial nerve during the technically demanding procedure. This finding can also be applied by surgeons who are performing laterally based open anterior capsulectomy.

This study had several limitations. The primary drawback lies within the cadaveric specimens. Mean specimen age was 82 years, and they were without elbow joint contractures. This may not accurately represent the distorted anatomy found in the stiff elbows that are usually indicated for arthroscopic anterior capsulectomy. Attempts were made at simulating live arthroscopy with constant inflow, using techniques such as pre-arthroscopy joint insufflation, gravity inflow during the arthroscopic portion, and joint re-insufflation with saline at the time of digital calibration measurements. However, these attempts might not have completely depicted actual arthroscopic conditions with the capsulectomy performed under inflow because they might have changed the anatomic position of the radial nerve, brachialis muscle, or MCL. The authors did not measure the thickness of brachialis muscle coverage of the radial nerve anterolaterally, but that has been previously studied by Omid et al.16

Conclusion

Based on these findings, an arthroscopic anterior capsulectomy can be performed as distal to the level of the proximal edge of the annular ligament, with the brachialis reliably protecting the radial nerve. This alternative, more distal, anterior capsulectomy at the level of the annular ligament is closer to the radial nerve but is still at a safe distance. The MCL was reliably distanced from the exiting point of the capsulectomy and can be safely considered to be at minimal risk with the proposed capsulectomy. In addition, the simple act of pronating the forearm during capsulectomy can aid in moving the radial nerve away from iatrogenic injury.

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Distance From Anterolateral Capsular Suture to Radial Nerve

SutureMean, mm (95% Confidence Interval)

PronationNeutralSupination
119.6 (15.8–23.4)18.8 (15.5–22.0)17.3 (13.6–21.0)
216.1 (12.5–19.7)14.8 (11.9–17.8)13.6 (10.0–17.2)

Change in Radial Nerve Distance to Capsule During Forearm Rotation

RotationMean, mm (P)

Suture 1 to CapsuleSuture 2 to Capsule
Pronation vs supination2.28 (≤.01)2.48 (≤.01)
Pronation vs neutral0.86 (.28)1.27 (.13)
Neutral vs supination1.46 (.03)1.24 (.07)

Distance From Medial Capsular Suture to Medial Collateral Ligament

SutureMean, mm (95% Confidence Interval)

PronationNeutralSupination
113.3 (10.5–16.1)12.9 (10.2–15.5)13.4 (10.4–16.4)
213.3 (9.5–17.0)13.8 (9.7–18.0)13.5 (9.6–17.4)

Change in MCL Distance to Capsule During Forearm Rotation

RotationMean, mm (P )

S1 MCL to CapsuleS2 MCL to Capsule
Pronation vs supination0.14 (.74)0.21 (.55)
Pronation vs neutral0.41 (.28)0.55 (.14)
Neutral vs supination0.55 (.29)0.34 (.37)
Authors

The authors are from the Department of Orthopaedics and Sports Medicine (KMC), University of Washington, Seattle, Washington; and the Department of Orthopaedics (MNG, SH, SAH), University of Maryland School of Medicine, Baltimore, Maryland.

The authors have no relevant financial relationships to disclose.

The authors thank Louis Okafor, MD, for providing the artwork for Figure 1 and Dori Kelly, MA, for professional manuscript editing.

Correspondence should be addressed to: S. Ashfaq Hasan, MD, Department of Orthopaedics, University of Maryland School of Medicine, 2200 Kernan Dr, Ste 1154, Baltimore, MD 21207 ( ahasan@som.umaryland.edu).

Received: March 28, 2019
Accepted: June 13, 2019
Posted Online: July 07, 2020

10.3928/01477447-20200619-07

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