The Epidemiology of Scapholunate Advanced Collapse

Abstract

Background: Scapholunate advanced collapse (SLAC) is the most common pattern of wrist arthritis. Sparse data exist regarding the SLAC wrist pattern of arthritis. This study aimed to document the epidemiology of advanced SLAC in terms of patients’ sociodemographics and possible association with trauma. Methods: Sixty-one patients with severe SLAC wrist were included. Baseline sociodemographic characteristics were reviewed. To evaluate the relationship to injury, this group of cases was compared with a control group of 61 patients with first carpometacarpal osteoarthritis (CMC OA). The following data were collected for both groups: age, gender, history of traumatic injury, history of manual labor, duration of symptoms, and dominant hand involvement. Pearson chi-square tests for categorical variables and independent samples t test for continuous variables were performed to determine differences between groups. Results: Patients with SLAC wrist were more likely to be male (80.3% vs 31.1%; p<0.001), have a history of a traumatic injury (69.5% vs 25.9%, P < .001), have longer symptom duration (10.3 ± 13.3 vs 3.5 ± 2.5 years, P = .001), be involved in a manual labor job (49.0% vs 20.0%, P = .002), and be younger (53.1 ± 10.4 vs 58.3 ± 9.8; P = .006) compared with patients with CMC OA. There was no difference in dominant hand involvement (49.2% vs 53.3%; P = .571) between the groups. Conclusions: This study identified the characteristics of patients with advanced SLAC wrist. Compared with a control cohort of CMC OA, patients with SLAC wrist were more likely to be male, have a history of a traumatic injury, and be younger.

Introduction

Scapholunate advanced collapse (SLAC) is a common arthritic pattern of the wrist, thought to result from attenuation of the scapholunate ligament leading to altered wrist kinematics. Watson and Ballet identified SLAC as the most common pattern of wrist arthritis, accounting for 57% of all cases in their initial series. This was followed by scaphotrapeziotrapezoidal (STT) arthritis in 27% of cases and a combined STT and SLAC pattern in 15% of patients.¹⁵ It is theorized that SLAC wrist pattern develops after an inciting event that leads to dissociation of the scaphoid and lunate. The resultant degenerative arthritic pattern is then thought to progress through 3 radiologic stages,¹⁶ and then a fourth stage of advanced pancarpal arthritis.¹⁷

The etiology of scapholunate ligament damage can be traumatic or atraumatic. Traumatic injury can result from a single acute event or multiple repeated events. Atraumatic causes of scapholunate ligament attenuation and development of subsequent SLAC wrist include calcium pyrophosphate dehydrate crystal deposition disease, rheumatoid arthritis, neuropathic diseases, and amyloid deposition diseases.^9,11

Although few documented cases of the natural history of scapholunate dissociation exist in the literature,^3,8 it is widely believed that SLAC progresses through the above mentioned stages of degenerative changes following scapholunate dissociation. Ultimately, following this progression to an advanced pattern of SLAC wrist, surgical intervention is often required. Various treatment options and their associated long-term outcomes are well established in the literature.^2,7,14 However, further data about the epidemiology of SLAC wrist deformity remain limited.^2,4,7 The objectives of this study were: (1) to describe the sociodemographic characteristics of patients with advanced SLAC wrist arthritis pattern (defined as those undergoing surgical intervention); and (2) to evaluate the presence of a possible association between SLAC and traumatic injuries.

Materials and Methods

Study Design

Study approval was obtained from the hospital institutional review board. A case-control study was designed with the case group defined as any patient undergoing a surgical procedure for SLAC between January 1, 2008, and January 1, 2013. A control group was selected from the same time period and same institution for patients undergoing a surgical procedure for first carpometacarpal osteoarthritis (CMC OA). A case-control study design was chosen to allow for comparison of factors, sociodemographic characteristics, and history of trauma, between two of the most common patterns of osteoarthritis of the hand and wrist. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines on observational studies were followed where applicable.¹³

First CMC OA was chosen as the control cohort as it is a very common arthritic pattern with well-known demographics.^1,10,12 It is known that asking specific questions in a case-control design can lead to recall bias. One method to control for this is to select a control group within a similar illness category that is not related to the association being investigated. Because first CMC OA is not typically associated with trauma and is prevalent, we chose this pattern of arthritis as the control. In addition, the referral base for arthritis of the thumb and wrist are likely similar, making first CMC OA a good pathology for the control group.

Data Source

A single tertiary care center’s operating room databases were obtained identifying all surgical procedures performed at our institution between January 1, 2008, and January 1, 2013. Patients undergoing surgical procedures for SLAC wrist were identified by searching the following procedure codes: arthrodesis/fusion wrist (including 4-corner fusion, midcarpal fusion), arthroplasty total wrist, and proximal row carpectomy, excision bone arm/hand (including radial styloidectomy). Subsequently, patient charts and radiographic images were reviewed to identify those patients with an underlying diagnosis of SLAC wrist.

The control group was identified from the same institution over the same time period. The control group was identified as patients who underwent trapeziectomy and ligament reconstruction, with or without tendon interposition. Of these patients, a random number generator was used to select patients with a diagnosis of CMC OA from the entire cohort identified until we reached a ratio of 1:1 with the SLAC group. Confirmation of underlying diagnosis of CMC OA was confirmed in all patients by chart review and radiographic images.

Sociodemographic Data

Detailed chart reviews were performed for both study groups. A standard data collection sheet was utilized to extract pertinent patient information for both the case (SLAC) and control (CMC OA) groups. Data collected included hand dominance, operative side, procedure, age at time of surgery, duration of symptoms, history, date, mechanism of trauma to the affected hand, occupation, and sex. History of trauma was based on information obtained from chart review and recorded if clearly indicated with an inciting event corresponding to the symptoms in the operated wrist. Manual labor jobs were defined as professions that involve lifting >10 kg intermittently (eg, manual laborer) or >2 kg repetitively (eg, grocery store clerk).

Statistical Analysis

Categorical variables were described using frequencies (percentages) and compared with Pearson chi-square tests. Continuous variables were presented as means (standard deviations) and compared with independent samples t tests. Odds ratios and 95% confidence intervals were calculated for dichotomous outcome data for patients in the SLAC group. Statistical significance was defined as P < .05. Missing data were minimized by extensive chart review.

Results

A total of 163 patients who had undergone one of the defined procedures for SLAC wrist over the specified time period were identified from the database. Of these patients, 61 had a confirmed diagnosis of SLAC wrist and were included in the study. The procedures performed on these patients were the following: proximal row carpectomy (n = 28), 4-corner fusion (n = 23), wrist arthrodesis (n = 8), and 2 patients with a scaphoid excision and lunocapitate fusion. For the control group, CMC OA patients, a total 483 patients were identified who had undergone ligament reconstruction in the defined time period. Of these patients, 61 were randomly selected for the control group. Patients in the control group (CMC OA) underwent variants of trapeziectomy and ligament reconstruction, with or without tendon interposition.

Characteristics for patients in each group are summarized in Table 1. Patients in the SLAC group were more likely to be male (80.3% vs 31.1%, P < .001), younger age at time of surgery (53.1 vs 58.3 years old, P = .006), have a positive history of traumatic injury (69.5% vs 25.9%, P < .00), be involved in manual labor jobs (49.0 % vs 20.0%, P = .002), and have a longer duration of symptoms prior to surgical intervention (10.3 vs 3.5 years, P = .001). No difference in involvement of the dominant hand was found between groups (49.2% vs 53.3%, P = .6). Patients with SLAC wrist had a significantly elevated odds ratio for male gender (9.0), history of trauma (6.5), and manual labor job (3.9) (Table 2).

Table 1.

Sociodemographic Characteristics of SLAC (Case) and CMC OA (Control) Patients.

Variables	Case (SLAC)	Control (CMC OA)	P value
	n = 61	n = 61
Age (years), mean (SD)	53.1 (10.4)	58.3 (9.8)	.006*
Dominant hand affected	30 (49.2)	32 (53.3)	.57
Male gender	49 (80.3)	19 (31.1)	<.001*
History of trauma	41 (69.5)	15 (25.9)	<.001*
Manual labor employment	25 (49.0)	10 (20.0)	.002*
Symptom duration (years), mean (SD)	10.3 (13.3)	3.5 (2.5)	.001*

Note. Values are frequencies (percentages) unless otherwise indicated. Percentages that do not add up to 100% are due to missing data or rounding. SLAC = scapholunate advanced collapse; CMC OA = carpometacarpal osteoarthritis.

^*P < .05.

Table 2.

Odds Ratios for SLAC Patients.

Variables	OR (95% CI)
Dominant hand affected	0.81 (0.38-1.70)
Male gender	9.03 (3.93-20.70)
History of trauma	6.53 (2.91-14.60)
Manual labor employment	3.94 (1.63-9.53)

Note. SLAC = scapholunate advanced collapse; OR = odds ratio; CI = confidence interval.

Discussion

This case-control study demonstrated that SLAC wrist was associated with a history of trauma. In our study, patients with severe SLAC wrist or requiring surgical intervention were found to generally be men in their sixth decade of life with a history of manual labor. These patients also reported traumatic injury–related symptoms for a period of approximately 10 years. These findings are in keeping with the profile of SLAC wrist patients in the literature.^2,4,7 An association between trauma and SLAC wrist was uncovered with the case-control design of this study by using a control cohort of patients who were treated for another common hand arthritic pattern. Patients included in the control cohort were comparable in age, involvement of the dominant hand, and gender to previously published studies on patients with advanced CMC OA.^1,5,6,12

Advantages of utilizing a case-control design was that it allowed us to compare a known case group (SLAC wrist) to a cohort of patients from the same study base with another common arthritic pattern (CMC OA). To maximize the validity of our results, patients in both groups were identified from the same tertiary referral center over the same time period. Comparison with another common arthritic pattern of the hand and wrist allowed us to identify characteristics unique to SLAC wrist and minimize the effects of variables leading to generalized arthritic patterns in the upper extremity. In addition, comparison to another arthritic pattern allowed us to minimize recall bias in assessing the traumatic etiology of SLAC pattern.

Symptom duration reported by patients with a SLAC wrist was significantly longer than those patients in the CMC OA group. Although recall bias cannot be excluded, it is unlikely that patients with SLAC wrist would preferentially recall a longer duration of symptoms than the control group. It could be theorized that this prolonged duration of symptoms may relate to the progression of SLAC wrist through the proposed radiologic stages until the symptoms resulted in the patient seeking surgical management.^15,17 Age at the time of surgical treatment of the two study groups was significantly different, with the SLAC wrist patients being significantly younger than CMC OA patients. Comparing age of onset of symptoms (by using age during treatment and symptomatic period) resulted in a 12-year difference between groups (SLAC 42.8 years, CMC OA 54.8 years). Although age is likely a risk factor for both patterns of OA in this study, a significant difference was found between the study group and control group suggesting that other factors are important in the development of SLAC wrist.

History of a traumatic injury to the affected upper extremity was significantly more common in patients with SLAC wrist than CMC OA. Given the two conditions studied, these results are not surprising because scapholunate injury is a known injury pattern. Although a significant association was found between traumatic injury and SLAC wrist, it cannot be inferred that the recalled trauma was the causative mechanism in the eventual development of SLAC wrist. It does however bring up the potential that injury can be a factor in the development of SLAC wrist.

Limitations of this study inherent to the case-control design specifically relate to data collection and the accuracy and completeness of the patient record. Recall bias, particularly with respect to the history taking regarding a traumatic event preceding the patient’s symptoms in the SLAC group could have some impact on the results. Although bias in data collection may be introduced in the initial history taking, no additional bias occurred from the data retrieval through chart review methods and standardized data recording sheets for both groups. We chose a control group from the same institution and time period undergoing a surgical procedure for another form of hand/wrist OA to minimize baseline differences between groups while also minimizing interview and recall bias. However, given the heterogeneity of etiology and presentation in both groups, unknown confounders may exist. The patient population in this study was derived from a tertiary referral center, and generalizability of these findings may not extend beyond a similar cohort.

In conclusion, this study revealed that patients with SLAC wrists were more likely to be younger, be male, and have a history of traumatic injury, when compared with CMC OA patients. Future prospective studies assessing the potential association of SLAC wrist and trauma should take place to corroborate our findings.