PIP Joint: Anatomy, Common Injuries, and Treatment

The proximal interphalangeal joint, commonly called the PIP joint, is the middle hinge of each finger, sitting between the knuckle and the fingertip joint. It is the most frequently injured joint in the hand and, when stiff or painful, one of the most functionally limiting. Despite being small enough to cover with a fingertip, the PIP joint relies on an intricate web of ligaments, tendons, and cartilage that work together to let you grip a coffee mug, type, or button a shirt. Understanding how it is built, how it breaks down, and what can be done about it matters whether you are recovering from a jammed finger or living with arthritis.

Where the PIP Joint Sits and What Holds It Together

Each finger (excluding the thumb, which has only two bones) has three joints. Starting from the palm, you have the metacarpophalangeal (MCP) joint at the knuckle, the PIP joint in the middle, and the distal interphalangeal (DIP) joint near the fingertip. The PIP joint connects the proximal phalanx (the finger bone closest to the palm) to the middle phalanx. It functions primarily as a hinge, bending and straightening the finger through a range that can exceed 100 degrees in a healthy hand.

The joint’s stability comes from several structures working in concert. On the palm side sits the volar plate (also called the palmar plate), a thick fibrocartilaginous structure firmly anchored to the base of the middle phalanx. Its proximal end is thinner and membranous, connected to the proximal phalanx through the check-rein ligaments, which act as secondary stabilizers against hyperextension.¹ On either side, the collateral ligaments and their accessory counterparts prevent the joint from wobbling sideways, while the A3 pulley helps suspend the volar plate laterally. Dorsally, the extensor mechanism drapes over the joint like a hood, channeling tendon forces that straighten the finger.

How the PIP Joint Straightens and Bends

Bending the PIP joint is relatively straightforward: the flexor tendons on the palm side pull the middle phalanx toward the palm. Extension, on the other hand, is surprisingly complex. The extensor digitorum communis (EDC) tendon on the back of the hand splits into three parts just past the knuckle. The central slip inserts directly into the base of the middle phalanx and pulls it straight. The two side branches, called lateral bands, combine fibers from both the EDC and the smaller intrinsic muscles of the hand (the interossei and lumbricals) before continuing down to the fingertip.

A cadaveric study found that the EDC contributes more to PIP joint extension than previously thought, because it delivers force through two pathways: the central slip and both lateral bands. The intrinsic muscles, by contrast, only reach the PIP joint through the lateral bands.² During flexion, the lateral bands shift toward the palm side, held in check by the transverse retinacular ligaments. When the finger straightens, they glide back to their dorsal position. That smooth back-and-forth translation is essential. When it fails, deformities follow.

Forces Acting on the Joint

For such a small joint, the PIP experiences significant mechanical loads. A modeling study of the index finger estimated mean contact pressures at the PIP joint of roughly 6 MPa during simulated pinch and grasp, comparable to the pressures seen at the larger knuckle joint.³ Earlier cadaveric work confirmed that the highest average contact pressures in the finger actually occur at the DIP joint near the fingertip, but the PIP joint is not far behind.⁴ These forces accumulate over a lifetime, which is part of why the PIP joint is a common site for osteoarthritis, especially in people who do heavy manual work.

Common Injuries

The PIP joint is the most frequently injured joint in the hand, and the mechanisms fall into a few recognizable patterns.

Volar Plate Injuries

A hyperextension force, the classic “jammed finger” from catching a ball or falling on an outstretched hand, tends to tear the volar plate at its distal attachment. Research has shown that virtually all pure hyperextension injuries rupture the volar plate at this end. When the tear does not involve a small bone chip visible on X-ray, it is easy to miss, and inadequate treatment can lead to a chronic hyperextension deformity.⁵ Ultrasound has emerged as a practical way to visualize volar plate damage in the acute setting, with findings that align well with what MRI shows.⁶

Collateral Ligament Tears

A sideways force on the finger can rupture one of the collateral ligaments. Complete tears sometimes cause noticeable swelling and a fusiform (spindle-shaped) appearance. Both surgical repair and non-operative treatment can restore joint stability, though surgical repair may speed functional recovery and reduce that persistent fusiform deformity.⁷

Boutonnière Deformity

When the central slip of the extensor tendon is disrupted, the PIP joint can gradually drop into a flexed position while the DIP joint hyperextends, producing what is known as a boutonnière deformity. The name comes from the French word for “buttonhole,” because the joint head pokes through the torn extensor mechanism the way a flower pokes through a lapel buttonhole. Importantly, a central slip tear alone is not enough to cause the full deformity; combined injury of the central slip, the triangular ligament, and fibers of the interosseous hood must occur together.⁸ When a collateral ligament tear is added on top of those injuries, the lateral band can displace so far toward the palm that the deformity becomes irreducible. In anatomical experiments, this displacement averaged about 11.5 mm, far enough that neither passive nor simulated active extension could correct it.⁹

Why PIP Joint Stiffness Matters So Much

A stiff PIP joint affects daily life more than you might expect. The PIP joint contributes the lion’s share of a finger’s total arc of motion. Research measuring how much joint motion is actually needed for common tasks found that functional PIP flexion averages about 60 degrees, meaning you need to bend the PIP joint to roughly that angle to handle everyday objects.¹⁰ A later study refined that range, finding that the PIP joint’s functional arc spans roughly 23 to 87 degrees, which represents about 59% of its total active motion.¹¹

What this means practically is that losing even 20 or 30 degrees of PIP motion can push you outside the functional window. A finger that cannot fully straighten will bump into things and struggle with flat surfaces like keyboards. A finger that cannot bend enough will have trouble gripping cylindrical objects or closing around a doorknob. The PIP joint’s outsized importance in hand function is one reason clinicians treat its injuries and contractures aggressively.

Arthritis and Inflammatory Conditions

The PIP joint is a frequent target of both osteoarthritis and inflammatory arthritis. In osteoarthritis, the cartilage wears down over time, leading to bony enlargements along the joint margins called Bouchard’s nodes. These are the PIP equivalent of Heberden’s nodes at the DIP joint. Pain, stiffness, and reduced grip strength follow. In rheumatoid arthritis, the disease process starts with synovial inflammation, and even with modern biologic medications that control the inflammation, progressive deformity of the small joints in the hands can still develop over time due to soft-tissue imbalance and loss of joint congruence.

Psoriatic arthritis has its own distinctive pattern at the PIP joint. Dactylitis, the diffuse “sausage digit” swelling characteristic of psoriatic arthritis, involves not just the joint lining but also the flexor tendons, the subcutaneous fibrous tissue, and the small entheses where ligaments and tendons anchor to bone.¹² This multi-structure involvement is why dactylitic fingers look uniformly swollen rather than just puffy at the joint line.

Conservative Treatment Options

For mild to moderate PIP joint problems, non-surgical approaches are the first line. Splinting, hand therapy, and injections each have a role, though the evidence base is thinner than you might hope.

Steroid Injections

Corticosteroid injection into the PIP joint can provide real but temporary relief for osteoarthritis. A study using X-ray-guided injections found significant improvements in both pain and range of motion lasting up to three months. Painkiller use dropped and hand function improved during that window. By six months, however, patients were drifting back toward their pre-injection baseline.¹³ That three-month ceiling is worth knowing: injections buy time and comfort, but they are not a long-term fix on their own.

Splinting and Orthoses for Flexion Contracture

When the PIP joint gets stuck in a bent position after an injury, splinting is the standard approach. Three main types of orthoses are used: dynamic splints (like the spring-loaded Capener design), static progressive splints (which are manually adjusted to hold the joint at its end range), and serial static casts (changed periodically as the joint loosens). A randomized trial comparing all three found no statistically significant differences in outcome, though there was a trend toward greater improvement in active extension with the dynamic Capener splint, and it required less total wear time at end range.¹⁴ A systematic review of the broader literature concluded that the evidence base is too heterogeneous to declare a winner, and more research is needed to guide clinicians on which orthosis to choose for which patient.¹⁵

In practice, the choice often comes down to patient tolerance and the therapist’s experience. Dynamic splints allow some movement during wear, which some people find more comfortable. Static progressive designs are simpler and less bulky. Serial casting is effective but requires regular clinic visits for adjustments. All three demand consistent compliance over weeks to months.

When Surgery Becomes Necessary

For a severely arthritic or destroyed PIP joint, replacement is an option. Three main implant materials are in use: silicone, pyrocarbon, and metal. The debate over which is best has been going on for decades, and the evidence is increasingly clear that silicone, the oldest option, holds up well against newer alternatives.

A meta-analysis comparing pyrocarbon and silicone implants found that pyrocarbon prostheses were associated with worse functional scores and higher pain scores than silicone.¹⁶ A separate systematic review and meta-analysis that also included metal implants found that metal prostheses achieved the greatest post-operative range of motion (about 67 degrees), followed by silicone (about 56 degrees) and pyrocarbon (about 46 degrees). But silicone had the best pain scores, and its complication rate of roughly 11% was notably lower than pyrocarbon (about 19%) and metal (about 22%). Survival rates did not differ significantly among the three.¹⁷

Earlier work comparing pyrocarbon resurfacing arthroplasty directly to silicone found that both provided excellent pain relief and comparable range of motion, with complications that were implant-specific rather than universally favoring one design.¹⁸ The bottom line for patients weighing their options is that silicone remains a reliable choice with a long track record, while newer materials offer theoretical advantages in joint mechanics but have not consistently outperformed silicone in real-world results. The final call depends on the patient’s age, activity level, and the surgeon’s experience with each implant system.

For severe joint destruction where replacement is not ideal, fusion (arthrodesis) is the other surgical option. Fusing the PIP joint eliminates pain by eliminating the joint surface entirely, but it sacrifices motion. It is most commonly considered for the index finger, where stability for pinch grip matters more than bending range, and less commonly for the ring and small fingers, where PIP motion is more critical for power grasp.

Camptodactyly and Congenital PIP Flexion Deformities

Not all PIP joint problems are acquired. Camptodactyly is a congenital flexion deformity of the PIP joint, most often affecting the small finger. It shows up in a bimodal pattern: either before age two or during the adolescent growth spurt after age ten.¹⁹ The underlying problem involves a range of structures, from the skin and fascia to the tendons and even the joint surface itself. One unifying theory holds that abnormalities of the extensor mechanism are the primary lesion, with the other soft-tissue changes following secondarily.

Treatment depends on severity. Mild deformities often respond to stretching and splinting alone, and surgery is generally reserved for contractures greater than about 60 degrees.²⁰ When surgery is performed, the approach matters. Simply lengthening the flexor tendon without addressing the extensor mechanism tends to fail. A study of severe congenital PIP contractures present at birth found that digits treated with extensor mechanism realignment and flexor tendon transfer improved reliably, while those treated with flexor lengthening alone did not improve at all.²¹ Even with successful surgery, some residual contracture is common, and post-operative splinting is considered essential to maintaining the correction.

Diagnosing PIP Joint Problems

Plain X-rays remain the starting point for any PIP joint complaint, revealing fractures, joint space narrowing, and bony deformities. But soft-tissue injuries, which account for the majority of PIP joint problems, do not show up on X-ray. MRI has long been the gold standard for visualizing volar plate tears, collateral ligament damage, and extensor tendon injuries. Increasingly, though, high-resolution ultrasound is proving to be a practical alternative. It is cheaper, faster, available in the clinic, and does not require the patient to lie still in a scanner. For volar plate injuries specifically, ultrasound findings have been shown to align well with MRI, making it a reasonable first-line imaging choice when the clinical question is whether the volar plate is intact.²²

For inflammatory conditions like psoriatic arthritis, ultrasound has an additional advantage: it can detect tendon sheath thickening, enthesitis, and increased blood flow from inflammation in real time. MRI is still superior for detailed structural assessment, but ultrasound’s convenience makes it especially useful for monitoring disease activity over repeated visits.