Robleh A. Omar OMS4¹; Micah Jones, DO^2 
1Edward Via College of Osteopathic Medicine
²Kleinert and Kutz/University of Louisville Adult Hand, Cincinnati Children’s Hospital Pediatric hand/upper extremity

Abstract

The Carpometacarpal (CMC) joint of the thumb is crucial for hand function and relies heavily on ligamentous stability. Osteoarthritis of the first CMC joint, also known as basilar thumb arthritis (BJA), is a common degenerative disease, particularly among the elderly and postmenopausal women. This paper aims to explore the effectiveness of nonoperative treatment modalities in managing BJA by offloading the basal joint. This is a comprehensive review of existing literature on nonoperative treatments for BJA, focusing on orthoses, activity modification, and ergonomic tools. The study involves a detailed analysis of clinical studies and reviews addressing the conservative management of BJA. Key treatment modalities, such as orthoses for joint stabilization, exercises for improving flexibility, and ergonomic tools for offloading the joint, are evaluated for their efficacy in pain relief and functional improvement. The findings of this review suggest modalities to offload the basal joint and improve daily function in patients with BJA. Orthoses provide joint stabilization and, while ergonomic modifications and exercises help offload the CMC joint, addressing the increased forces experienced by the joint. Despite the prevalence of BJA, there is a significant gap in research on conservative management, highlighting the need for further studies to optimize non-surgical treatment strategies.

Introduction
The Carpometacarpal (CMC)  joint of the thumb is a saddle-shaped joint that relies heavily on ligamentous stability. 

Osteoarthritis of the first CMC joint also known as basilar thumb arthritis, and basal joint arthritis, is a degenerative disease of the first CMC joint. Typical symptomatology includes pain at the base of the thumb with activities such as pinching and loading the basal joint. Pain is commonly caused by twisting doorknobs, opening jars, turning car keys among other common activities. In the context of basal joint arthritis, it’s crucial to consider the impact of hand positions on the integrity and stress levels experienced by the carpometacarpal (CMC) joint, particularly the dorsal CMC ligament complex. A flat hand position, often used in various daily activities, can place significant stress on the dorsal CMC ligament complex. This increased stress may exacerbate the symptoms of basal joint arthritis, leading to pain and further joint degeneration. Understanding and mitigating the stress on this ligament complex through ergonomic hand positioning and supportive orthotics can be beneficial in managing the condition and preventing further deterioration. The diagnosis of CMC osteoarthritis can be made with a history of pain at the basal joint, pain with physical examination maneuver sensitive for BJA (such as the lever test, grind test, or metcarpophalangeal extention test), and a positive radiographic reading¹. Positive radiographic findings can include joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts as described later in this paper. Radiographic imaging is also useful in determining the severity of the disease. In general treatment can be conservative with adjusting activities of daily living, or operative depending on factors such as symptom severity and the stage of the disease. For the sake of uniformity, this disease will be referred to as basal joint arthritis (BJA).

Epidemiology
BJA is a very common arthritis of the hand. In terms of prevalence, it is only second to distal interphalangeal joint (DIP) arthritis. BJA is seen in 25% of men and 40% of women over the age of 75 years old². This disease is more common in women and Caucasians. Postmenopausal women in their fifth to sixth decade of life are at increased risk compared to men of similar age. This is thought to be due to hormonal influences². 

Pathoanatomy
The pathophysiology of BJA is due to attenuation of volar, dorsal, and ulnar ligaments which have been named as primary stabilizers of the CMC joint. This joint has unique demands and is prone to arthritis due to many factors as presented by Ladd et al. These factors include joint instability, ligament laxity, and repetitive stress as key contributors. There is evolutionary pressure for a less constrained joint, delicate kinematics, and large compressive loads with activity, as well as hormonal influences related to sex and age³. Metacarpal phalangeal hyperextension deformity is a compensatory change that is commonly seen in patients. The patho-mechanics related to metacarpophalangeal (MCP) hyperextension play a significant role. The hyperextension of the MCP joint can lead to increased stress on the CMC joint, particularly when the dorsal ligament complex becomes attenuated. This attenuation reduces the stability of the CMC joint, often resulting in subluxation. Over time, this misalignment can worsen the wear and tear on the joint surfaces, exacerbating the symptoms of CMC arthritis. The first CMC joint is biconcave saddle joint. There are four articulations of the joint as can be seen in Figure 1⁴. These consist of the Trapezimetacarpal, trapeziotrapezoid, scaphotreapezial, and the trapezium-index metacarpal. 

Figure 1

There is very important ligamentous stabilization that surrounds the CMC joint. The Anterior oblique ligament also known as the volar beak ligament is the primary stabilizing force that counteracts the tendency for the CMC joint to go into subluxation. The intermetacarpal ligament is the primary restraint for radial translation of the 1^st metacarpal. The dorsoradial ligament is the primary restraint to dorsal dislocation and is commonly injured during dislocation of the CMC dorsally. The posterior oblique ligament is also visible in Figure 2⁵ below. Interestingly due to the biomechanics of the saddle joint, pinch force is applied 13x more in the basal joint⁶. This is important to consider when discussing modalities to offload the joint.

Figure 2

Classification of BJA
The most used classification system for Basilar thumb arthritis is the Eaton and Littler Classification system⁷. This system divides the progression of BJA into a stepwise progression ranging from stage 1- stage 4. Stage 1 consists of slight joint space widening, articular contours are normal, and there is <1/3 subluxation. Stage 2 shows slight narrowing of the CMC joint with sclerosis, significant capsular laxity, 1/3 subluxation of the joint, and osteophytes <2mm. Stage 3 displays mild narrowing of the CMC joint with osteophytes, >1/3 subluxation of the joint, and osteophytes > 2mm. Stage 4 has severe degenerative changes, major subluxation of the joint, very narrow joint space, cystic and sclerotic subchondral bone changes, significant erosion of the scaphotrapezial joint, and importantly there will be pantrapezial arthritis. Examples of these stages can be seen in Figure 3⁸.

Figure 3

Imaging
Radiographic imaging is important to diagnose the stage of BJA. The recommended view is an AP, Lateral and Roberts view. The Roberts view is when the x-ray beam is centered on the trapezium and the metacarpal with the thumb flat on the table. The thumb will also be hyper pronated. This positioning can be seen in figure 4⁹.

Figure 4

Treatment Options
Nonoperative treatment is the first line of treatment for BJA. Lopez et al. found in a long term outcomes cohort study that non-operative treatment strategies showed positive outcomes for no worsening of pain or limitations in activities of daily living after 12 months¹¹. Treatment options that will not be discussed include injections, CMC arthroscopic debridement, 1^st metacarpal osteotomy, trapeziectomy +/- ligament reconstruction, CMC arthrodesis, CMC denervation, and CMC prosthetic arthroplasty¹⁰. This paper will serve as a reference for modalities to offset the need for surgical intervention and alleviate symptoms while patients are still in the mild-moderate symptom stages. The offloading techniques can also be used by patients who have had injections, and prior surgical procedures as well. 

According to a systematic review performed by Spaans Et al., There are only a few high-quality studies addressing the conservative treatment of BJA. These studies suggest some effect of orthoses and intra-articular hyaluronate or steroid injections¹². Orthoses support the thumb in abduction and support inherent stability by maximizing the thumb web space. Pain management is achieved if the splint is worn for longer than three months. Daytime pain relief is possible even if only worn at night¹³_.  Examples of these splints can be seen in Figure 5¹³.

Figure 5

Exercises are recommended to aid in improving joint flexibility and range of motion. These exercises are designed to strengthen the muscles around the CMC joint, improve joint stability, and reduce strain on the ligaments, particularly the dorsal ligament complex. By targeting the muscles that support the thumb, these exercises can help prevent MCP hyperextension, decrease the likelihood of subluxation at the CMC joint, and ultimately alleviate pain and slow the progression of arthritis. Exercises should be done routinely to maintain the benefits gained¹⁴. Various exercises exist but any exercise done should be done slowly and smoothly. Exercises should not cause pain and can be supplemented with rest and stretching¹⁵. Examples of some exercises can be seen in Figure 6¹⁶.

Figure 6

Offloading the basal joint is important because the thumb CMC joint experiences up to 13 times the force transmitted at the tip of the thumb¹⁷. An arthritis cup is any cup that augments the grip so that the CMC joint is not stressed. These can include cups with a wider thick gripped handle, specially designed cups designed to drink from two hands, as well as handles that can be added to any thermos to augment the gripping experience. Examples of these respective modalities can be seen in Figure 7. These modalities are inexpensive and widely attainable for patients with online shopping or through brick and mortar department stores. 

Figure 7

Another option to offload the basal joint that is especially useful for those patients who work at a desk is to use an ergonomic mouse and keyboard. The traditional mouse that is used with computers exacerbates the pinch mechanism which loads the first CMC joint. Pain can also be managed by using an ergonomic keyboard. By using an ergonomic mouse such as the one pictured in figure 8, the basal joint will be significantly offloaded by decreasing the pinching force that is required when using a standard mouse. Holding the keyboard in a position that maintains the webspace and abduction will also provide comfort. There is little research providing evidence to support the usage of these modalities, however it may be reasonable to attempt these changes as they are very low risk.

Figure 8

Changes can also be made when the patient is writing. There are many different techniques to lessen the amount of strain that is placed upon the basal joint during the writing process. One of these techniques is to start to use wider grip pens and pencils that require decreased pinch strength to operate. There are also attachments that can be added to existing pens and pencils to facilitate decreased pinch strength as well. These can be seen in Figure 9¹⁸. Finally, by changing the traditional grip of the pencil to hold the pencil between the 2^nd and 3^rd phalanges, there is a decreased load placed upon the first CMC joint and decreased pinch as well.

Figure 9

Conclusion
BJA is a debilitating disease that has well defined operative interventional research. There is however a lack of research surrounding non-operative modalities to off load the first CMC joint. Non-operative modalities are the first line treatment for the management of this disease and should be implemented prior to surgical intervention. Many modalities to off load the basal joint were explored including orthoses, activity modification, exercises, ergonomic office supplies, and changes to writing techniques. There is a need for research on the efficacy of non-operative treatment modalities to recommend the best non-surgical management for patients.

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