Abstract
Objective
Open arthrolysis (OA) combined with hinged external fixator (HEF) is a promising surgical option for patients with elbow stiffness. This study aimed to investigate elbow kinematics and function following a combined treatment with OA and HEF in elbow stiffness cases.
Methods
Patients treated with OA with or without HEF due to elbow stiffness were recruited between August 2017 and July 2019. Elbow flexion‐extension motion and function (Mayo elbow performance scores, MEPS) were recorded and compared between patients with and without HEF during a 1‐year follow‐up period. Additionally, those with HEF were assessed by dual fluoroscopy at week 6 postoperatively. Flexion‐extension and varus‐valgus motions, as well as ligament insertion distances of the anterior medial collateral ligament (AMCL) and lateral ulnar collateral ligament (LUCL), were compared between the surgical and intact sides.
Results
This study included 42 patients, of which 12 with HEF demonstrated a similar flexion‐extension angle and range of motion (ROM) and MEPS as the other patients. In patients with HEF, the surgical elbows showed limitations in flexion‐extension (maximal flexion, 120.5° ± 5.3° vs 140.4° ± 6.8°; maximal extension, 13.1° ± 6.0° vs 6.4° ± 3.0°; ROM, 107.4° ± 9.9° vs 134.0° ± 6.8°; all Ps < 0.01) compared with the contralateral sides. During elbow flexion, a gradual valgus‐to‐varus transition of the ulna, increase in the AMCL insertion distance, and steady change in the LUCL insertion distance were observed, with no significant differences between the bilateral sides.
Conclusions
Patients treated with OA and HEF demonstrated similar elbow flexion‐extension motion and function to those treated with OA alone. Although the use of HEF could not restore an intact flexion‐extension ROM and might result in some minor but not significant changes in kinematics, it contributed to clinical outcomes comparable to that of the treatment with OA alone.
Keywords: Ankylosis, Elbow, External fixator, Kinematics
Patients treated with open arthrolysis (OA) and hinged external fixator (HEF) demonstrated similar elbow flexion‐extension motion and Mayo elbow performance scores to those treated with OA alone. Although the use of HEF could not restore an intact flexion‐extension range of motion and might result in some minor but not significant changes in kinematics, it contributed to clinical outcomes comparable to that of the treatment with OA alone.
Introduction
The elbow is sophisticatedly structured by three relatively independent articulations: humeroulnar, humeroradial, and proximal radioulnar joints. Flexion/extension, varus/valgus, and pronation/supination are involved in controlling the spatial positions of the forearm and hand. The elbow is also notorious for being the most prone to stiffness after injury or surgery. 1 , 2 In order to adapt to modern lifestyles, a range of motion (ROM) of approximately 120° in flexion‐extension (from 27° ± 7° flexion to 149° ± 5° flexion) and another ROM of approximately 120° in pronation‐supination (from 20° ± 18° pronation to 104° ± 10° supination) are necessary, which may be greater than previously reported. 3 Open arthrolysis (OA) is a conventional surgical option for elbow stiffness that fails to respond to conservative treatments. To restore functional ROM, removal of the ossified tissue, resection of the contracted capsule, and release of the medial and lateral collateral ligaments are often performed. In cases of severe stiffness, detachment and subsequent reattachment of the ligaments may be required. Therefore, the use of a hinged external fixator (HEF), which protects the ligaments from overloading, is a reliable option for maintaining the stability of the humeroulnar joint in the early postoperative period. 4 , 5 , 6 , 7 , 8 , 9
Despite some widely reported satisfactory clinical outcomes, there have been concerns regarding the restriction of HEF on elbow motion. 10 , 11 To our knowledge, the single‐plane HEF is the most commonly used in clinical practice, which allows ulnar movements in the flexion‐extension plane but restricts movements in the varus‐valgus plane or around the pronation‐supination axis. 12 Biomechanical evidence has shown that the rotation axis is not perfectly consistent during elbow flexion/extension. Thus, even if carefully placed according to bony landmarks, the single‐plane HEF will inevitably cause increased resistance at full flexion or extension, which can result in limited ROM. 10 , 13 To date, most biomechanical studies on HEF have been cadaveric, with the elbow loaded with external force. As a result, it has not been fully elucidated whether the application of HEF alters elbow kinematics, such as flexion‐extension, varus‐valgus, and pronation‐supination motions, changes in joint space and ligament length, and function restoration.
Conventionally, motion capture system that applies skin surface trackers has been used in kinematic study. However, due to relatively large soft‐tissue artifacts, this method is insufficient of accuracy in terms of joint kinematics. In recent years, the use of dual fluoroscopy has improved the accuracy in joint kinematics measurement non‐invasively. It is a two‐dimensional‐to‐three‐dimensional (3D) positioning technology. By using the X‐ray of bone structures in two intersecting directions and subsequently manipulating 3D bone models to match the bony outlines on the X‐ray images, the in vivo motion of bones can be quantified with sub‐millimeter and sub‐degree accuracy. 14 , 15 Our study was aimed to: (i) investigate the in vivo kinematics of the elbow following combined treatment with OA and single‐plane HEF using dual fluoroscopy in patients with elbow stiffness; and (ii) compare elbow motion and function between patients with and without HEF. To the best of our knowledge, very few studies have used a dual fluoroscopic imaging system to measure in vivo elbow kinematics, and this study is the first to evaluate the kinematics following HEF placement.
Methods
Patient Enrollment
The participants were recruited among patients who underwent treatment with OA due to unilateral elbow stiffness at Shanghai Sixth People's Hospital between August 2017 and July 2019. The inclusion criteria were: (i) follow‐up ≥12 months; (ii) closure of the elbow epiphysis; (iii) no history of upper limbs deformity and asymmetry; and (iv) achievement of an ROM from 0° extension to 140° flexion intraoperatively. The exclusion criteria were: (i) existing factors that affect elbow mobility, such as articular steps, cartilage damage, and so on; and (ii) inaccurate model‐image matching. Informed consent regarding the potential radiation dose and possible benefits was obtained from the patients prior to the assessment. This study was approved by the Ethics Committee of Shanghai Sixth People's Hospital (YS‐2017‐89).
Surgical Procedure and Postoperative Management
A combined medial and lateral approach was used in each case. Capsular adhesion release and removal of osteophyte and heterotopic ossification were routinely performed. Detachment and reattachment of the proximal insertion of the collateral ligament were performed when the regular release was unsatisfactory. If contractured collateral ligaments were also released, making the elbow potentially unstable, HEF (Careway Ltd., Shanghai, China; or Stryker Corp., Kalamazoo, MI, USA) would be applied (Fig. 1). Passive ROM from 0° extension to 140° flexion should be achieved intraoperatively by the gravity of the forearm or with minimal external force. Before placement of the HEF, a guide pin was carefully implanted under fluoroscopy according to the landmarks of the anatomic rotation axis. Early rehabilitation was planned based on the degree of soft tissue swelling.
Fig. 1.
X‐ray images before and after a combined treatment with open arthrolysis and hinged external fixator. Preoperative (A) and postoperative (B) images of a 30‐year‐old male who suffered from elbow stiffness 6 months after internal fixation of humeral fracture. Preoperative (C) and postoperative (D) images of a 49‐year‐old male who sustained elbow stiffness 9 months after internal fixation of olecranal fracture.
Modeling and Coordinate System Establishment
After the surgery, the patients treated with OA and HEF underwent clinical computed tomography (SIMENS Corp., Berlin, Germany) of the bilateral upper limbs in the supine position with elbows flexed at 90° and hands pronated, resulting in images of 1‐mm thickness, 512 × 512‐pixel density, and 0.98 × 0.98 mm pixel size. CT images were then imported into the Mimics software (Materialise Corp., Leuven, Belgium) to generate 3D models of the humerus and ulna using bone segmentation and smoothing options. The bony landmarks of the anatomical rotation axis were manually marked, including the anteroinferior site of the medial epicondyle (H1) and the tendon insertion on the lateral epicondyle (H2). The apex of the sublime tubercle (U1) and the intersection of the radial notch and supinator crest (U2) were also marked. The proximal and distal insertions of the anterior medial collateral ligament (AMCL) and lateral ulnar collateral ligament (LUCL) were uniformly determined at H1 and U1, as well as at H2 and U2, respectively (Fig. 2A).
Fig. 2.
(A) Elbow rotation axis and bony landmarks. (B) Humeral and ulnar local coordinate systems. (C) Scene of dual‐fluoroscopic assessment. (D) Schematic diagram of model‐image matching. H1, anteroinferior medial epicondyle; H2, lateral epicondyle; H3, medial epicondyle; U1, the apex of sublime tubercle; U2, the intersection of radial notch and supinator crest.
The local coordinate systems (CS) of the humerus and ulna were established according to the recommendations of the International Society of Biomechanics. 16 To define humeral CS, the origin (Oh) was first determined at the midpoint between the medial and lateral epicondyles (H3 and H2), and the y‐direction was defined as the vector pointing proximally from Oh towards the great tuberosity. The x‐direction is defined as the forward vector perpendicular to the plane formed by the y‐axis and the connecting line of both epicondyles. Finally, the z‐direction was determined as the common vector perpendicular to the x‐ and y‐directions, pointing to the right (Fig. 2B). For the ulnar CS, the origin (Ou) was consistent with Oh, the y‐axis was defined as the line pointing proximally from the ulnar styloid process to the Ou, and the x‐ and z‐directions were similarly defined as previously described (Fig. 2B). The rotation of the ulna relative to the humerus was decomposed in the Z‐X‐Y sequence, resulting in three rotation angles representing the flexion‐extension, pronation‐supination, and varus‐valgus motions of the ulna.
Dual‐Fluoroscopic Assessment
Patients treated with OA and HEF were assessed by dual fluoroscopy at week 6, immediately before HEF removal. The raw fluoroscopy image is usually distorted because the tube device generates diverging rather than parallel X‐rays that penetrate the object to be filmed. Thus, a self‐developed calibration plate was used to measure the distortion and derive undistorted images. The plate was X‐ray transparent, with dozens of embedded steel beans placed in a grid pattern and equally spaced in the horizontal and vertical directions. Before the assessment, two C‐arms were placed angularly (approximately 90°) to allow the X‐ray from one machine to intersect the X‐ray from the other, forming a common testing zone. Subsequently, a positioning device with a known geometry was filmed in the testing zone to calculate the relative orientations of the two machines. During the assessment, patients were seated on a chair to allow their elbows to be comfortably placed on an X‐ray permeable platform in the testing zone (Fig. 2C). First, low‐dose fluoroscopy was performed to ensure that the elbows were adequately viewed by the two C‐arms; that is, clearly and entirely filmed, centrally placed, and without major obscures. The C‐arms then started to film at a rate of 30 frames/s, during which patients were requested to perform elbow flexion at a constant rate from maximal extension to flexion. The fluoroscopic duration was approximately 3–5 s for each side, and the mean radiation dose was 3.1 mSv for each patient.
Ten to 15 frames were selected from each task for the analysis. First, the image distortion was calibrated. Second, a projection relationship simulating the dual‐fluoroscopic setting was calculated, by which two projection images of the 3D model were generated. Third, the orientation of the 3D model was manually manipulated to match the virtual projections perfectly with the outlines on the fluoroscopic images; thus, the relative orientation of the two bones was restored (Fig. 2D). Finally, the ulnar movement relative to the humerus and the distance between ligament insertions were calculated. Because of the minimal axial rotation of the ulna (<5°) and the relatively low accuracy in detecting such motion, pronation‐supination was not included in the analysis. Data processing was performed using MATLAB software (MathWorks Corp., Natick, MA, USA). 17
Clinical and Kinematic Indicators
Clinical indicators included angular and functional indexes. Angular indexes, including flexion/extension angle and ROM, were measured and recorded by an assistant at baseline and at 6 and 12 months postoperatively. Functional index, the Mayo elbow performance score (MEPS), was measured at baseline and final follow‐up. See details of our previous study. 18 In patients treated with OA and HEF, varus‐valgus angle of the ulna relative to the humerus, and the ligament insertion distance of the AMCL and LUCL, were measured from the intact and surgical sides using dual fluoroscopy.
Statistical Analysis
Comparisons between patients with and without HEF were performed using Student's t‐test for continuous variables and the chi‐square test for categorical variables. Using the flexion‐extension angle as an independent variable, the varus‐valgus angle and ligament insertion distance were interpolated at an interval of 5° to allow for comparisons between the surgical and intact sides, and a paired t‐test was used for the comparison. Statistical analysis was performed using the Stata software (Stata Corp., College Station, TX, USA). Statistical significance was set at P < 0.05.
Results
Patient Information and Comparison between Groups
From August 2017 to July 2019, this study included 54 patients, of whom 16 were treated with OA and HEF and 38 with OA only. Finally, 42 patients (mean age 38.8 ± 14.1 years, range 19–73 years) were eligible for the study. No significant differences in age, sex, maximal flexion‐extension angle, ROM, or MEPS were found between patients treated with and without HEF (Table 1).
TABLE 1.
Comparison of demographic, motion, and function data
| Indexes | OA + HEF (n = 12) | OA (n = 30) | P value |
|---|---|---|---|
| Age (years) | 40.5 (12.4) | 38.1 (14.9) | 0.620 |
| Sex (male) | 66.6% | 43.3% | 0.172 |
| Baseline | |||
| Maximal FE (°) | 92.9 (21.3)/52.1 (19.4) | 100.8 (12.3)/45.0 (17.1) | 0.138/0.250 |
| FE ROM (°) | 40.8 (24.0) | 55.8 (21.0) | 0.051 |
| MEPS | 43.3 (4.4) | 46.7 (7.0) | 0.135 |
| Six weeks postoperative | |||
| Maximal FE (°) | 120.5 (5.3)/13.1 (6.0) | 120.0 (11.4)/13.7 (8.0) | 0.885/0.821 |
| FE ROM (°) | 107.4 (9.9) | 106.3 (15.4) | 0.824 |
| Twelve months postoperative | |||
| Maximal FE (°) | 124.2 (14.3)/19.6 (12.5) | 130.5 (11.4)/12.7 (10.0) | 0.138/0.067 |
| FE ROM (°) | 104.6 (25.7) | 117.8 (17.5) | 0.060 |
| MEPS | 83.8 (9.6) | 88.8 (9.9) | 0.137 |
Note: Data are shown as mean (standard deviation) or percentage. OA, open arthrolysis; HEF, hinged external fixator; FE, flexion‐extension; ROM, range of motion; MEPS, Mayo elbow performance score
Flexion‐Extension Motion
In patients treated with OA and HEF, the surgical elbows showed limitations in flexion‐extension motion (maximal flexion, 120.5° ± 5.3° vs 140.4° ± 6.8°, P < 0.001; maximal extension, 13.1° ± 6.0° vs 6.4° ± 3.0°, P = 0.005) and ROM (107.4° ± 9.9° vs 134.0° ± 6.8°, P < 0.001) compared with the intact sides at 6 weeks postoperatively (Fig. 3). The intact sides shared a common ROM of 10°–132° flexion, and the common ROM for the surgical sides was 19°–116°.
Fig. 3.
Comparison of elbow flexion‐extension motion. Data are shown as mean and standard deviation.
Varus‐Valgus Motion
As shown in Fig. 4, the mean valgus angle was 10.4° ± 3.8° for the intact sides at 10° flexion and 11.3° ± 7.4° for the surgical sides at 20° flexion, and the mean varus angle was 3.9° ± 6.6° for the intact sides at 130° flexion and 1.2° ± 7.3° for the surgical sides at 115° flexion. A gradual transition from valgus to varus was observed on the intact and surgical sides during elbow flexion, and the reverse occurred at approximately 100° of flexion. The varus‐valgus angle of the surgical sides was closer to the values of the intact sides in the middle phase of flexion than in early or deep flexion. However, no significant differences were observed during the course.
Fig. 4.
Varus‐valgus motion of the ulna in elbow flexion. Data are shown as mean ± standard deviation.
Collateral Ligament Insertion Distance
Figure 5A shows an increase in AMCL insertion distance on both sides during elbow flexion. On the intact sides, the AMCL insertion distance increased variably from 16.1 ± 1.2 mm at 10° flexion to 22.2 ± 2.8 mm at 130° flexion; on the surgical sides, it increased uniformly from 17.4 ± 3.6 mm at 20° flexion to 22.7 ± 3.1 mm at 115° flexion. On average, the AMCL insertion distance on the surgical sides was 1.1 mm longer than that on the intact side, but no statistical differences were observed.
Fig. 5.
Ligament insertion distance during elbow flexion. (A) Anterior medial collateral ligament (AMCL). (B) Lateral ulnar collateral ligament (LUCL). Data are shown as mean ± standard deviation.
Figure 5B shows a steady change in the LUCL insertion distance during flexion, with a variation range of less than 2 mm. On the intact sides, the LUCL insertion distance varied from 26.6 ± 2.4 mm to 28.3 ± 3.0 mm; on the surgical sides, it varied from 27.1 ± 2.2 mm to 28.8 ± 3.2 mm. A slight increase in the LUCL insertion distance was observed for both sides from extension to 100° flexion, while the values of the intact side, but not the surgical side, showed a decline in deep flexion. Likewise, no significant differences in the LUCL insertion distance were observed between the two sides.
Discussion
According to our clinical evaluation, patients treated with OA and HEF could also restore a satisfactory ROM that was comparable to that of cases without HEF, which meant that the rotation guide pin was correctly placed; otherwise, HEF would become a block for elbow motion. 13 , 14 Kinematic studies have confirmed some minor rotations around the varus‐valgus axis and internal‐external rotation axis, which cannot be accurately measured by traditional motion capture devices, such as maker‐based optical capture systems, owing to soft tissue artifacts. Steel bean‐embedded stereo radiographic imaging is the gold standard for measuring bone motion in vivo and has an accuracy of sub‐millimeter and sub‐degree. The reported accuracy of the image‐matching‐based dual fluoroscopic imaging system can also reach a comparable level, and it has the superiority of non‐invasion, making it easier for participants to accept.
Extension‐Flexion Motion
An average ROM from 13.1° extension to 120.5° flexion was observed in patients who received the combined treatment with OA and HEF due to elbow stiffness, which was significantly limited compared to their intact sides but markedly improved compared to the preoperative ROM. In a cadaveric study, Stavlas et al. 10 reported mean extension of 19.5° ± 7.2° and 19.1° ± 6.6° in lateral collateral ligament‐deficient and medial/lateral collateral ligament‐deficient elbows, respectively, after HEF placement. The authors attributed the limitation of the extension to the rigidity of the HEF and the deviation of the guide pin positioning from the actual rotation axis. Even though the placement of the guide pin was in strict accordance with the standard method, 19 the in vivo operation might be more affected by factors such as a limited surgical field, indistinct anatomic landmarks, and inconvenience of fluoroscopy. However, the limitation of extension reported in our study was slightly lower than that reported in the cadaveric study, which might be due to the potential influence of muscle strength. We considered that the driving moment generated in active flexion could be greater than the load (3 N·m) adopted in the cadaveric experiment. In addition, ROM can be influenced by the degree of preoperative stiffness, intraoperative release, and postoperative rehabilitation.
Varus‐Valgus Motion
A gradual transition from valgus to varus was found in elbow flexion, the tendency and magnitude of which were similar to those reported in the literature. 20 The results showed that the varus‐valgus angle of the surgical sides changed in an almost linear fashion, indicating lower compliance in varus‐valgus motion compared with the intact sides. The surgical sides tended to be more extraversive (non‐significant) than the intact sides in the early and terminal phases of flexion, which suggests that even minor off‐axial motion could lead to increased resistance to extension/flexion after HEF placement. In this regard, multi‐plane‐designed HEF, such as the Compass Hinge (Smith & Nephew Corp., London, England), should be superior to single‐plane HEF. However, whether such minor alterations in varus‐valgus motion lead to clinically significant changes and whether multi‐plane HEF provides better clinical outcomes remain to be elucidated.
Collateral Ligament Insertion Distance
Besides rotational movement, displacement between bones is also important in joint kinematics. It reflects the stability of the joint. Proper displacement indicates good stability of the joint, which is of great significance for the healing of the ligament after repair. Excessive displacement suggests joint laxity, which will adversely affect prognosis. The direct manifestation of elbow instability is an abnormal joint space, which is difficult to measure because it is the distance between two curved surfaces rather than two distinct points. Therefore, we used the collateral ligament insertion distance, which is an estimation of ligament length, to make an indirect judgment of elbow laxity. Previous studies have suggested that elbow instability can be judged when the varus/valgus angle is 10° greater than the contralateral side or when the humeroulnar joint space exceeds 4 mm. 21 In this study, both the varus/valgus angle and the collateral ligament insertion distance supported good elbow stability.
We also noticed that the HEF was not 100% rigid in practice, as evidenced by a minor swing off of the rotation plane during elbow flexion, which may be attributed to the reduced structural stiffness caused by the deformation of the joint connection. Thus, HEF has been regarded as a semi‐rigid immobilization method. 12 The ideal HEF should be able to eliminate abnormal stresses in the bone and joint and ensure that the collateral ligament is in an appropriate range of tensile stress; otherwise, postoperative rehabilitation will be difficult, and patients will suffer from pain in active and/or passive motions. 22
Limitations and Strengths
This study has some limitations. First, the sample size is small. Therefore, the results may not be sufficiently robust and should be carefully interpreted. Clinical evidence from a larger sample is required to validate this preliminary study. Second, some participants had a history of elbow fractures. The altered morphology caused by the fracture placed new challenges that studies of intact bone had not met, which, however, might affect the accuracy of the method compared with studies using a normal bone model. More patience and efforts were needed during manual image matching. Finally, after HEF placement, the surgical sides could not perform full ROM in flexion, and pronation/supination of the forearm was restrained because of obstruction of the ulnar module. Therefore, additional forms of elbow motion were not included in this analysis.
There are also strengths. To the best of our knowledge, this study is the first to investigate elbow kinematics following the placement of HEF, which would gain biomechanical insight into this promising technique. In addition, this study is one of the few to introduce dual fluoroscopy to the measurement of in vivo kinematic of the elbow and preliminarily demonstrates the feasibility of this technique in elbow kinematic measurement.
Conclusion
In this study, patients treated with OA and HEF demonstrated similar elbow flexion‐extension motion and function as those treated with OA alone. Although the use of HEF could not restore a full flexion‐extension ROM as the intact sides and might resulted in some minor but not significant changes in kinematics, it contributed to clinical outcomes comparable to that of the treatment with OA alone.
Authors' Contributions
Conceptualization: H.H., C.B. and D.J.; Methodology: L.M. and H.H.; Investigation: L.M., L.Z. and H.H.; Formal Analysis: L.M. and L.Z.; Resources: W.Y., C.M., Y.W., L.S. and P.Y.; Writing ‐ Original Draft: L.M., W.Y. and L.S.; Writing ‐ Review & Editing: L.Z., C.M., Y.W., P.Y. and D.J.; Visualization: L.M.; Supervision: C.B. and D.J.; Funding Acquisition: D.J. All the authors have read and approved the manuscript.
Conflict of Interests
All the authors declare no conflict of interests.
Ethics Statement
This study was approved by the Ethics Committee of Shanghai Sixth People's Hospital (YS‐2017‐89). Informed consents were obtained from all the patients.
Acknowledgments
This work was supported by the Foundation of Shanghai Collaborative Innovation Center for Translational Medicine (TM201918).
Ming Ling and Zhenming Liang contributed equally to this work.
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