The aim of the study was to assess phosphorus (P) concentration in structures of the knee joint—including the tibial spongy bone, articular cartilage, meniscus, anterior cruciate ligament, and infrapatellar fat pad (Hoffa’s fat pad)—of patients following knee joint replacement. The study also aimed to assess the influence of selected biological and environmental factors on P concentration in studied parts of the knee joint. Phosphorus concentration was determined using inductively coupled plasma-atomic emission spectrometry (ICP-AES). Statistically significant differences in P concentration were found between different elements of the knee joint. The highest P concentration was measured in the spongy bone (72,746.68 mg kg−1 dw) and the lowest in the Hoffa’s fat pad (1203.19 mg kg−1 dw). P levels were unaffected by gender, age, BMI, place of residence, smoking, or alcohol consumption. Data on P concentration in the osteoarticular elements of the knee may be useful in the interpretation and evaluation of biochemical, morphological, and mechanical changes occurring in the body.