A partial knee replacement, medically known as Unicompartmental Knee Arthroplasty (UKA), addresses arthritis confined to only one section of the knee joint. Unlike a total knee replacement, UKA leaves healthy joint parts untouched, replacing only damaged cartilage and bone with prosthetic components. Patients often worry about post-operative pain. Understanding the surgical differences and modern pain management protocols confirms that pain is not only manageable but is often significantly less severe than with a full joint replacement.
Reduced Pain Due to Less Invasive Surgery
A partial knee replacement generally results in less immediate post-operative pain due to its minimally invasive nature. The procedure is highly targeted, meaning surgeons only remove diseased bone and cartilage from the affected compartment, typically the medial (inner) side. This preservation of healthy tissue minimizes trauma to surrounding structures, which is the primary source of acute pain after surgery.
UKA is performed through a smaller surgical incision, often measuring only a few inches, compared to the longer incision needed for a total knee replacement. The procedure explicitly preserves both the anterior and posterior cruciate ligaments (ACL and PCL). Keeping these ligaments intact is important because they contain sensory nerves, and their preservation maintains the knee’s natural mechanics. Less disruption to bone and soft tissue correlates directly with a reduced inflammatory response and lower acute pain levels immediately following the procedure.
Modern Multimodal Pain Management Strategies
Modern orthopedic care employs multimodal analgesia, using a combination of pain medications working through different mechanisms to control discomfort effectively. This approach begins before the incision, known as pre-emptive pain management, to reduce the nervous system’s sensitivity to pain signals. This active management keeps pain controlled enough to allow the patient to begin movement and physical therapy almost immediately after the procedure.
A primary element is the use of peripheral nerve blocks, such as the adductor canal block, administered just before surgery to numb the affected leg for up to 24 hours. This block provides profound pain relief during the most acute post-surgical period, significantly lowering the initial need for strong narcotic medication. Once the nerve block wears off, the patient transitions to a scheduled regimen of non-opioid medications, including non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen. These medications work to combat the inflammation and general soreness that follows any surgical procedure.
Opioids are reserved for “breakthrough pain” only when other methods are insufficient and are prescribed for short-term, low-dose use. By attacking pain from multiple angles—nerve signaling, inflammation, and central perception—this multimodal protocol ensures a smoother recovery. The goal is to keep the patient comfortable enough to participate in rehabilitation, which is a major factor in reducing long-term pain.
Expected Timeline for Post-Surgical Pain
The intensity of pain following a partial knee replacement follows a predictable chronological pattern, helping set realistic expectations for recovery.
Acute Pain Phase
The acute pain phase typically lasts for the first one to three days, with peak discomfort occurring within the first 24 hours. Pain during this period is often described as a deep, throbbing ache. It is primarily managed by the nerve block and hospital-administered pain protocols.
Sub-Acute Phase
As the nerve block dissipates and the patient transitions home, they enter the sub-acute phase, lasting from the first week up to about four to six weeks. Pain shifts from intense surgical pain to generalized soreness, swelling, and discomfort, especially during activity and physical therapy. Adherence to the scheduled oral pain regimen is important during this time to manage inflammation and allow for necessary movement.
Residual Pain Phase
The residual pain phase extends from one to three months, sometimes longer, characterized by intermittent discomfort that is often activity- or weather-related. Patients commonly report pain after prolonged standing, walking, or a feeling of stiffness in the morning. This pain gradually diminishes as surrounding muscles strengthen and the body accepts the implant. Most individuals resume daily activities with reduced pain within six weeks, and discomfort continues to fade over the following months.
The Role of Physical Therapy in Pain Reduction
Physical therapy (PT) is a necessary component of recovery and plays an active role in the ultimate reduction of pain after a UKA. While early exercises can cause muscle soreness and stretching discomfort, this sensation is distinct from the original surgical pain and indicates healing and progress. The immediate goal of PT is to restore the full range of motion, particularly achieving full knee extension. This prevents long-term stiffness that can be a source of chronic pain.
Pre-habilitation, which involves strengthening the muscles around the knee before surgery, also contributes to a smoother, less painful post-operative experience. Stronger supporting muscles mean less muscular weakness and a faster return to normal movement patterns afterward. Adherence to the prescribed rehabilitation schedule directly correlates with a faster recovery and a reduction in reliance on pain medication. By improving joint function and muscle strength, physical therapy ensures the long-term success of the replacement.